Color converter and color converting method

ABSTRACT

The present invention relates to processes of color data, and an object of the present invention is to provide a color converter and color converting method, with a color converting process for enhancing the saturation for color data, capable of preventing the influences of noise components from being emphasized and also preventing damaged color from occurring.  
     In order to achieve the object, multiplication coefficient calculation means ( 4 ) calculates a multiplication coefficient based on characteristic information of first color data which is a target of color conversion, and second color correction amount calculation means ( 5 ) calculates a second color correction amount by multiplying a first color correction amount by the multiplication coefficient obtained from first color correction amount calculation means ( 1 ). Then, in color correction amount addition means ( 2 ), the second color correction amount is added to the first color data, so that second color data after the color conversion is obtained. Since the second color correction amount is calculated on the basis of the first characteristic information, it is possible to prevent the influences of noise components from being emphasized, and also to prevent damaged color from occurring.

TECHNICAL FIELD

[0001] The present invention relates to a full-color printing relatedapparatus such as a printer, a video printer and a scanner, animage-processing apparatus for forming computer graphics images, orcolor-data-processing apparatuses to be used in display devices such asmonitors, and more particularly, concerns a color converter that carriesout a color conversion process on color data and a color convertingmethod.

BACKGROUND ART

[0002] In general, for example, in a full color printing relatedapparatus such as a printer, a video printer and a scanner, animage-processing apparatus for forming computer graphics images, ordisplay devices such as monitors, a color conversion process is carriedout on color data that constitute image data to be inputted to such adevice.

[0003] The color conversion process in printing is an essentialtechnique for correcting image-quality degradation caused by a colormixing property due to ink that does not have a pure color and anon-linear property of printed images and for outputting a printed imagehaving good color reproducibility. Moreover, in a display device such asa monitor, when an image is displayed on the basis of inputted colordata, a color conversion process is carried out so as to output(display) an image having desired color reproducibility in accordancewith conditions of use, etc. of the device. Conventionally, with respectto the system for such a color conversion process, two kinds of systems,that is, a table conversion system and a matrix operation system, arelisted.

[0004] Typical examples of the table conversion system include athree-dimensional look-up table system. In this system, for example,color data of red, green and blue or complementary color data of yellow,magenta and cyan (hereinafter, sometimes indicated as “Y, M, C”), whichhave been color corrected in accordance with values of color data thatare subjects of color conversion represented by, for example, R, G, B(hereinafter, sometimes indicated as “R, G, B”), are preliminarilystored in a look up table that is constituted by a memory such as a ROM.When color data to be subjected to color conversion is inputted, thecolor data or complementary color data, which has been color-convertedin accordance with the value, is extracted from a look up table, andoutputted. In this method, the color data or complementary color data tobe stored in the look up table is selected and adjusted so that adesired conversion characteristic can be adopted; thus, the resultingadvantage is that it becomes possible to carry out a color conversionprocess that is superior in color reproducibility.

[0005] However, in such a simple arrangement in which data that has beencolor-converted on the basis of each of combinations of inputted colordata is stored, the look up table requires a large capacity memory ofapproximately 400 Mbit. For example, Japanese Patent ApplicationLaid-Open No. 63-227181 (1988) has disclosed a compression method of amemory capacity; however, even in this method, a memory as great asapproximately 5 Mbit is required. Therefore, this system has problems inthat, since a large capacity memory is required, it is not possible toconstitute the color converter by using LSIs, and in that it isdifficult to allow data that is stored in the memory to flexibly adaptto a change in conditions in use, etc.

[0006] Moreover, in the matrix operation system, for example, in thecase where, on the basis of image data having the first color data, Ri,Gi, Bi, to be subjected to color conversion, the second color data Ro,Go, Bo that have been color-converted are found, the following equation(1) serves as a basic operation expression. $\begin{matrix}{\begin{bmatrix}{R\quad o} \\{G\quad o} \\{B\quad o}\end{bmatrix} = {\left( {A\quad i\quad j} \right)\begin{bmatrix}{R\quad i} \\{G\quad i} \\{B\quad i}\end{bmatrix}}} & {{Equation}\quad (1)}\end{matrix}$

[0007] In equation (1), Aij represents a coefficient matrix, and in Aij,i=1 to 3 and j=1 to 3. As indicated by equation (1), this system makesit possible to calculate the second color data by carrying out thematrix operation on the first color data; therefore, different from theabove-mentioned table conversion system, it is not necessary to storedata that corresponds to each of combinations of inputted color data.Thus, it becomes possible to avoid the problem caused by the necessityof a large capacity memory such as seen in the table conversion system.

[0008] Here, in general, desired color reproduction by the use of colorconversion includes “faithful color reproduction” and “preferable colorreproduction”. “Faithful color reproduction” refers to colorreproduction that is faithful to an actual color, and with respect to amethod for achieving this reproduction, the standard such as NTSC andsRGB may be used or a color reproducing process may be carried out byusing standard color spaces. In contrast, “preferable colorreproduction” refers to color reproduction in which human visualsensation characteristics and color memory are taken into consideration,that is, color reproduction which is desirably sensed by the humanbeing; thus, this is not necessarily coincident with “faithful colorreproduction”.

[0009] For example, in the case of color reproduction in displayed TVimages, in most cases, “preferable color reproduction” is carried out.In the color memory of the human being, for example, the color of thesky and the color of green lawn tend to be memorized with colors thatare clearer, and have higher saturation than the actual colors.Therefore, in order to achieve “preferable color reproduction”, ingeneral, a color conversion process is carried out in a manner so as tomake the saturation of a color higher than the inputted color data. Inthe faithful color reproduction also, there are many cases in which acolor conversion process is carried out in a manner so as to make thesaturation of a color higher than the inputted color data.

[0010] Moreover, the color data to be inputted to an image displayapparatus or the like is not necessarily coincident with the originalcolor data that is generated by a color-data generating device such as acamera. This is because color data is subjected to various noises whileit is transmitted.

[0011] For example, suppose that the original color data, generated by acamera, are transmitted through a transfer path, and inputted to animage display device. Here, it is assumed that the original color dataoutputted from the camera are Rs, Gs, Bs that are respective color datarepresenting red, green and blue. Further, it is assumed that the colordata to be inputted to an image display device through the transfer pathare Ri, Gi, Bi. In other words, if the color data are not subjected toinfluences of noise through the transfer path and if the transmittingand receiving sequences at the time of the transfer process are carriedout correctly, Rs=Ri, Gs=Gi and Bs=Bi are supposed to be satisfied.

[0012] However, in the actual transfer path, the data are susceptible toinfluences from noise. Moreover, any error might occur in thetransmitting and receiving sequences. In this case, supposing that noisecomponents including noise and errors that give influences on therespective color data of red, green and blue are Rn, Gn, Bn, the colordata Ri, Gi, Bi to be inputted to the image display device arerepresented by Ri=Rs+Rn, Gi=Gs+Gn and Bi=Bs+Bn. In other words, thecolor data Ri, Gi, Bi to be inputted to the image display device arerepresented by sums between the original color data components, Rs, Gs,Bs, and the noise components, Rn, Gn, Bn.

[0013]FIG. 24 shows an example of the original color data components,Rs, Gs, Bs, noise components, Rn, Gn, Bn and color data components Ri,Gi, Bi to be inputted to the image display device, in the case where thenoise components are smaller than the original color data components. Inthis Figure, the axis of ordinates represents the size of signals. Here,it is assumed that each of the color data components representing red,green and blue and the noise components is represented by an integer ina range of 0 to 255. Moreover, FIG. 24(a) shows the original color datacomponents, Rs, Gs, Bs, generated by a camera or the like, in whichRs=192, Gs=64 and Bs=64. FIG. 24(b) shows an example of the noisecomponents, Rn, Gn, Bn, in which Rn=8, Gn=8 and Bn=24. FIG. 24(c) showsthe color data components Ri, Gi, Bi to be inputted to the image displaydevice at this time. As described above, Ri, Gi, Bi of FIG. 24(c) areobtained from the sums of Rs, Gs, Bs shown in FIG. 24(a) and Rn, Gn, Bnshown in FIG. 24(b), so that Ri=200, Gi=72 and Bi=88.

[0014] As indicated by FIG. 24(a), the original color data, Rs, Gs, Bs,exhibit a red color in this example. In contrast, it is found that thecolor data, Ri, Gi, Bi, to be inputted to the image display device,shown in FIG. 24(c), exhibit a slightly bluish red color due to theinfluences of noise components Rn, Gn, Bn.

[0015] Moreover, FIG. 25 shows an example of the original color datacomponents, Rs, Gs, Bs, noise components, Rn, Gn, Bn and color datacomponents Ri, Gi, Bi to be inputted to the image display device, in thecase where the noise components are greater than the original color datacomponents (that is, the case when the original color data componentsare smaller). In this Figure also, the axis of ordinates represents thesize of signals. Furthermore, FIG. 25(a) shows an example of theoriginal color data components, Rs, Gs, Bs, in which Rs=24, Gs=8 andBs=8. FIG. 25(b) shows an example of the noise components, Rn, Gn, Bn,in which Rn=8, Gn=8 and Bn=24 in the same manner as FIG. 24(b). FIG.25(c) shows the color data components Ri, Gi, Bi to be inputted to theimage display device at this time, and these are represented by the sumsof Rs, Gs, Bs shown in FIG. 25(a) and Rn, Gn, Bn, shown in FIG. 25(b),so that Ri=32, Gi=16 and Bi=32.

[0016] The original color data components Rs, Gs, Bs, shown in FIG.25(a), exhibit a red color. In contrast, the color data, Ri, Gi, Bi, tobe inputted to the image display device shown in FIG. 25(c), have theblue color component of color data emphasized due to the influences ofnoise components Rn, Gn, Bn, thereby exhibiting a magenta color with agreat change in the hue.

[0017] As indicated by the comparison between FIG. 24 and FIG. 25, whenthe noise components become greater than the original color datacomponents, changes in characteristics (hue, brightness, saturation andthe like) between the original color data and color data to be inputtedto the image display device become greater due to influences by noisecomponents. In other words, when the values of the original color datacomponents, Rs, Gs, Bs, are small, as in the case of color data in adark portion of an image, that is, when the brightness of the originalcolor data is low, the influences of the noise components Rn, Gn, Bnbecome very strong.

[0018] Here, the following description will discuss a case in which, inorder to achieve “preferable color reproduction” in an image displaydevice, a color conversion process is carried out on each of inputtedcolor data Ri=Rs+Rn, Gi=Gs+Gn and Bi=Bs+Bn by using a matrix operationsystem so as to increase the saturation of color. In this case, asindicated by the above-mentioned equation (1), simultaneously as thecolor conversion process for increasing the saturation is carried out oneach of the original color data Rs, Gs, Bs, it is also carried out oneach of the noise components Rn, Gn, Bn. In other words, when the colorconversion process for increasing the saturation is carried out on eachof the color data Ri, Gi, Bi containing noise components Rn, Gn, Bn,both of the saturation of the original color data components Rs, Gs, Bsand the saturation of the noise components Rn, Gn, Bn are increased.

[0019] Therefore, in particular, in the case where the original colordata components Rs, Gs, Bs are small with the noise components, Rn, Gn,Bn, being relatively great, such a color conversion process mainlyincreases the saturation of each of the noise components Rn, Gn, Bn. Inother words, the color conversion process tends to greatly emphasize theinfluences from noise and errors. The resulting problem is that in thecolor conversion device using the matrix operation system, influencesfrom noise and influences from errors relating to transmitting andreceiving processes become conspicuous in a portion having a lowbrightness in each of the original color data components Rs, Gs, Bs,that is, in a dark portion of an image.

[0020] As described above, in particular, in the case of a colorconversion process that is carried out on color data at a portion inwhich the original color data components are small with low brightness,careful consideration should be given so as not to emphasize theinfluences of noise and the influences of errors relating totransmitting and receiving processes. However, in the conventional colorconverting method using the matrix operation system as defined by theabove-mentioned equation (1), since no consideration is given to thecharacteristics such as brightness of color data to be inputted to theimage display device, it is not possible to solve the problem in whichthe influences of noise components become conspicuous at a dark portionin an image.

[0021] The following description will discuss a color converter usingthe conventional matrix operation system. FIG. 26 shows a block diagramshowing the configuration of a color converter using the conventionalmatrix operation system. In FIG. 26, reference numeral 101 is colorcorrection amount calculation means, and 102 is color correction amountaddition means.

[0022] The above-mentioned equation (1) is also represented by thefollowing equation (2), and its color conversion process is achieved bythe arrangement of the color converter shown in FIG. 26. $\begin{matrix}\begin{matrix}{\begin{bmatrix}{R\quad o} \\{G\quad o} \\{B\quad o}\end{bmatrix} = {{\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}\begin{bmatrix}{R\quad i} \\{G\quad i} \\{B\quad i}\end{bmatrix}} + {\left( {{A1}\quad i\quad j} \right)\begin{bmatrix}{R\quad i} \\{G\quad i} \\{B\quad i}\end{bmatrix}}}} \\{= {\begin{bmatrix}{R\quad i} \\{G\quad i} \\{B\quad i}\end{bmatrix} + {\left( {{A1}\quad i\quad j} \right)\begin{bmatrix}{R\quad i} \\{G\quad i} \\{B\quad i}\end{bmatrix}}}}\end{matrix} & {{Equation}\quad (2)}\end{matrix}$

[0023] In the coefficient matrix A1ij in equation (2), i=1 to 3, and j=1to 3.

[0024] The first color data Ri, Gi, Bi that are subjected to colorconversion are inputted to the color correction amount calculation means101. In the color correction amount calculation means 101, colorcorrection amounts R1 a, G1 a, B1 a that correspond to the first colordata Ri, Gi, Bi are calculated through a linear operation shown in thefollowing equation (3), and the resulting values are outputted to thecolor correction amount addition means 102. $\begin{matrix}{\begin{bmatrix}{R1a} \\{G1a} \\{B1a}\end{bmatrix} = {\left( {{A1}\quad i\quad j} \right)\begin{bmatrix}{R\quad i} \\{G\quad i} \\{B\quad i}\end{bmatrix}}} & {{Equation}\quad (3)}\end{matrix}$

[0025] Moreover, the first color data Ri, Gi, Bi are also inputted tothe color correction amount addition means 102. The color correctionamount addition means 102 adds the color data Ri, Gi, Bi and the colorcorrection amounts R1 a, G1 a, B1 a, and outputs the resulting secondcolor data Ro, Go, Bo after the color conversion. Here, as describedabove, in the conventional color-conversion device, upon calculation ofthe color correction amounts R1 a, G1 a, B1 a by the color correctionamount calculation means 101, the characteristics such as brightness ofthe first color data Ri, Gi, Bi to be inputted thereto are not takeninto consideration.

[0026] In this manner, in the color converter using the conventionalmatrix operation system, the color conversion process is carried outwithout taking the characteristics such as brightness of the first colordata Ri, Gi, Bi to be inputted to the device into consideration. Forthis reason, the same color conversion process is carried out in both ofthe cases in which, for example, color data components are small withinfluences of noise components being strongly exerted thereon and inwhich color data components are great with influences of noisecomponents being weakly exerted on color data. Thus, when a colorconversion process for increasing the saturation of the color data iscarried out, that is, when a color-emphasizing process is carried out,the influences are further emphasized at a dark portion of the imagethat is seriously susceptible to the influences of noise components. Forthis reason, instead of improving the image, the color-conversionprocess causes a defective image to be displayed on an image displaydevice or the like.

[0027] Another problem is that since the color-conversion process iscarried out without taking the characteristics of the first color dataRi, Gi, Bi to be inputted to the color converter into consideration,so-called “damaged color” in which fine color differences disappear inbright colors due to the color conversion tends to occur. Referring tospecific examples, the following description will discuss this problemin detail. In the following description, it is assumed that respectivecolor data components are represented by integers in a range from 0 to255, and that in the results of matrix calculations, first decimal incolor data is rounded to the nearest whole number.

[0028] Here, in a coefficient matrix in the operation carried out by thecolor correction amount calculation means 101 of the color convertershown in FIG. 26, that is, the coefficient matrix A1ij in theabove-mentioned equations (2) and (3), is represented by values shown inthe following equation (4). $\begin{matrix}{\left( {{A1}\quad i\quad j} \right) = \begin{bmatrix}0.2 & {- 0.1} & {- 0.1} \\{- 0.1} & 0.2 & {- 0.1} \\{- 0.1} & {- 0.1} & 0.2\end{bmatrix}} & {{Equation}\quad (4)}\end{matrix}$

[0029] In this case, for example, when Ri=230, Gi=20, Bi=20 are inputtedas the first color data, the results of calculations are Ro=272, Go=−1,Bo=−1, if no limitation is given to the range in which the second colordata Ro, Go, Bo are located. However, since Ro, Go, Bo are integers inthe range of 0 to 255, the second color data to be actually outputtedfrom the color converter are: Ro=255, Go=0, Bo=0.

[0030] Moreover, when the first color data, Ri=240, Gi=15, Bi=15, areinputted, Ro=285, Go=−8, Bo=−8 are supposed to be given, if nolimitation is given to the range in which the second color data Ro, Go,Bo are located. However, since the second color data, Ro, Go, Bo areintegers in the range of 0 to 255, the actual values are: Ro=255, Go=0,Bo=0.

[0031] In this manner, in the conventional color converter, the valuesof the second color data, obtained in the case where the first colordata, Ri=230, Gi=20, Bi=20, are inputted, become the same as the valuesof the second color data obtained in the case where the first colordata, Ri=240, Gi=15, Bi=15 are inputted. In other words, in both of thecases in which Ri=230, Gi=20, Bi=20 and in which Ri=240, Gi=15, Bi=15,the same color is displayed on the image display device, failing toexpress the difference in colors originally exists between the two data.

[0032] As described above, when the color conversion process is carriedout on the basis of the matrix operation system without taking thecharacteristics of the color data Ri, Gi, Bi to be inputted to thedevice into consideration, damaged color in which fine color differencesdisappear in colors having high brightness tends to occur.

[0033] Moreover, this damaged color also tends to occur when a colorconversion process for further enhancing the saturation of a color iscarried out on color data that is originally high in the saturation.Referring to specific examples, the following description will discussthis problem.

[0034] The saturation Sat of color data represented by, for example, R,G, B, is defined by the following equation (5) by using MAX (R, G, B)that are maximum values of R, G, B and MIN (R, G, B) that are theminimum values thereof.

sat=(MAX(R, G, B)−MIN(R, G, B))/MAX(R, G, B)   Equation (5)

[0035] Supposing that R, G, B are represented by integers from 0 to 255,the mono-color of red is represented by R=255, G=0, B=0, with itssaturation being represented by Sat=1. Moreover, white is represented byR=255, G=255, B=255, with its saturation being represented by Sat=0. Asalso indicated by equation (5), in an attempt to enhance the saturationSat, it is proposed to increase the value of MAX (R, G, B)−MIN(R, G, B).

[0036] Therefore, the saturation Sati of Ri, Gi, Bi to be inputted tothe image display device is represented by the following equation (6) onthe basis of the definition of equation (5):

sati=(MAX(Ri, Gi, Bi)−MIN(Ri, Gi, Bi))/MAX(Ri, Gi, Bi)   Equation (6)

[0037] In the same manner, the saturation Sato of color data Ro, Go, Boto be obtained by a color conversion process is represented by thefollowing equation (7):

sato=(MAX(Ro, Go, Bo)−MIN(Ro, Go, Bo))/MAX(Ro, Go, Bo)   Equation (7)

[0038] Here, in an attempt to increase the saturation of color dataafter color conversion by the color converter shown in FIG. 26, thecoefficient matrix A1ij of the above-mentioned equation (2) is set tovalues indicated by the following equation (8). $\begin{matrix}{\left( {{A1}\quad i\quad j} \right) = \begin{bmatrix}0.2 & {- 0.2} & {- 0.2} \\{- 0.2} & 0.2 & {- 0.2} \\{- 0.2} & {- 0.2} & 0.2\end{bmatrix}} & {{Equation}\quad (8)}\end{matrix}$

[0039] In this case, suppose that, for example, Ri=255, Gi=128, Bi=128are inputted to the converter shown in FIG. 26 as the first color data.At this time, the outputted second color data are represented by Ro=255,Go=77, Bo=77. In this case, the saturation Sati of the first color dataRi, Gi, Bi is approximately 0.5 on the basis of the above-mentionedequation (6), and the saturation Sato of the second color data Ro, Go,Bo is 0.7 on the basis of the above-mentioned equation (7). In otherwords, the saturation of the color data is enhanced by the colorconversion process.

[0040] Here, suppose that the first color data, Ri=255, Gi=26, Bi=26 areinputted. At this time, the saturation Sati of the first color data Ri,Gi, Bi is 0.9. In this case, if no limitation is given to the range inwhich Ro, Go, Bo are located, the second color data are represented byRo=296, Go=−25, Bo=−25. However, since Ro, Go, Bo are integers in therange of 0 to 255, the second color data are actually outputted asRo=255, Go=0, Bo=0.

[0041] Moreover, suppose that the first color data, Ri=255, Gi=51, Bi=51are inputted. At this time, the saturation Sati of the first color dataRi, Gi, Bi is 0.8. In this case, if no limitation is given to the rangein which Ro, Go, Bo are located, the second color data are representedby Ro=286, Go=0, Bo=0. However, since Ro, Go, Bo are integers in therange of 0 to 255, the second color data are actually outputted asRo=255, Go=0, Bo=0.

[0042] In this manner, the values of the second color data Ro, Go, Boobtained in the case where the first color data are Ri=255, Gi=26, Bi=26are the same as those values of the second color data Ro, Go, Boobtained in the case where the first color data are Ri=255, Gi=51,Bi=51. In other words, in both of the cases in which Ri=255, Gi=26 andBi=26 and in which Ri=255, Gi=51 and Bi=51, the same color is displayedon the image display device, failing to express a difference in colorsthat the two data originally have.

[0043] As described in the above-mentioned examples, when thecolor-conversion process is carried out by using a matrix operationsystem, without taking the characteristics of color data Ri, Gi, Bi tobe inputted to the color converter into consideration, damaged color inwhich fine color differences disappear in colors with high saturationtends to occur.

[0044] As described above, the following problems have been raised inthe conventional color converter. First, in the case where a colorconverter is arranged by a table conversion system using a memory suchas a ROM, a large capacity memory is required, and the resultingproblems are that it is not possible to constitute the color converterby using LSIs, and that it is not possible to flexibly change theconversion characteristics.

[0045] Here, in the case where the color converter is arranged by usinga matrix operation system, it is not necessary to store data with alarge capacity, making it possible to avoid problems that have beencaused by the necessity of a large capacity memory in the colorconverter in the table conversion system. However, when a colorconversion process for enhancing the saturation of the color data iscarried out, problems tend to arise, in which: influences of noisecomponents are further emphasized in the case of color data that havelow brightness and are susceptible to the influences of noisecomponents, or damaged color which fails to express fine colordifferences in colors having high brightness or in colors having highsaturation tends to occur.

DISCLOSURE OF THE INVENTION

[0046] The present invention has been devised in order to solve theabove-mentioned problems, and an object thereof is to provide a colorconverter and color converting method capable of preventing theinfluences of noise components from being emphasized in colors havinglow brightness and also preventing damaged color from occurring incolors having high brightness or high saturation, while capable offlexibly changing the conversion characteristics without the necessityof a large capacity memory, in a case where a color conversion processis carried out so as to enhance the saturation of color data inputted tothe device.

[0047] In a first aspect of a color correcting device according to thepresent invention, a color converter which carries out color correctionon first color data to convert to second color data corresponding to thefirst color data, including: first color correction amount calculationmeans for calculating a first color correction amount on the basis ofthe first color data by using a matrix computing system; multiplicationcoefficient calculation means for calculating a multiplicationcoefficient on the basis of characteristic information of the firstcolor data; second color correction amount calculation means forcalculating a second color correction amount by multiplying the firstcolor collection amount by the multiplication coefficient; and colorcorrection amount addition means for calculating the second color databy adding the second color correction amount to the first color data.

[0048] In a second aspect of the color correcting device according tothe present invention, the characteristic information of the first colordata is brightness.

[0049] In a third aspect of the color correcting device according to thepresent invention, the value of the multiplication coefficientcalculated by the multiplication coefficient calculation means becomessmaller as the brightness becomes smaller than a predetermined value.

[0050] In a fourth aspect of the color correcting device according tothe present invention, the value of the multiplication coefficientcalculated by the multiplication coefficient calculation means becomessmaller as the brightness becomes larger than a predetermined value.

[0051] In a fifth aspect of the color correcting device according to thepresent invention, the characteristic information of the first colordata is saturation.

[0052] In a sixth aspect of the color correcting device according to thepresent invention, the value of the multiplication coefficientcalculated by the multiplication coefficient calculation means becomessmaller as the saturation becomes larger than a predetermined value.

[0053] In a seventh aspect of the color correcting device according tothe present invention, the color converter further includescharacteristic information calculation means for calculating thecharacteristic information on the basis of the first color data.

[0054] In an eighth aspect of the color correcting device according tothe present invention, the characteristic information calculated by thecharacteristic information calculation means is brightness of the firstcolor data, and the brightness is calculated as a sum of values obtainedby multiplying the respective components of the first color data bypredetermined coefficients.

[0055] In a ninth aspect of the color correcting device according to thepresent invention, the characteristic information calculated by thecharacteristic information calculation means is brightness of the firstcolor data, and the brightness is calculated as the maximum value of thecomponents of the first color data.

[0056] In a tenth aspect of the color correcting device according to thepresent invention, the characteristic information calculated by thecharacteristic information calculation means is saturation of the firstcolor data, and the saturation is calculated on the basis of adifference between the maximum value of the components of the firstcolor data and the minimum value of the components of the first colordata.

[0057] In an eleventh aspect of the color correcting device according tothe present invention, the multiplication coefficient calculation meansincludes a look up table storing the multiplication coefficientcorresponding to the characteristic information.

[0058] In a twelfth aspect of the color correcting device according tothe present invention, the first color data and the first colorcorrection amounts are respectively Ri, Gi, Bi and R1, G1, B1corresponding to three primary color signals of red, green and blue, andthe first color correction calculation means includes: maximumvalue/minimum value calculation means for calculating the minimum valueα and the maximum value β of the first color data; hue data calculationmeans for calculating six hue data: r=Ri−α, g=Gi−α, b=Bi−α, y=β−Ri,m=β−Gi and c=β−Ri, respectively relating to red, green, blue, yellow,magenta and cyan, from the first color data and the minimum value α andmaximum value β calculated by the maximum value/minimum valuecalculation means; effective operation term calculation means forcalculating, by using the hue data and a predetermined coefficients ap1to ap6 and aq1 to aq6, a first effective operation term T2 having only avalue which is not zero among h1r=MIN (y, m), h1g=MIN (c, y) and h1b=MIN(m, c) or a zero value when all the h1r, h1g and h1b are zero, a secondeffective operation term T4 having only a value which is not zero amongh1y=MIN (r, g), h1c=MIN (g, b) and h1m=MIN (b, r) or a zero value whenall the h1y, h1c and h1m are zero, and a third effective operation termT5 having only a value which is not zero among h2ry=MIN (aq1×h1y,ap1×h1r), h2rm=MIN (aq2×h1m, ap2×h1r), h2gy=MIN (aq3×h1y, ap3×h1g),h2gc=MIN (aq4×h1c, ap4×h1g), h2bm=MIN (aq5×h1m, ap5×h1b) and h2bc=MIN(aq6×h1c, ap6×h1b) or a zero value when all the h2ry, h2rm, h2gy, h2gc,h2bm and h2bc are zero; coefficient generation means for calculating acoefficient matrix Uij on the basis of the minimum value α and maximumvalue β calculated by the maximum value/minimum value calculation means;and matrix operation means for carrying out the following matrixoperation: $\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {\left( {U\quad i\quad j} \right)\begin{bmatrix}{T2} \\{T4} \\{T5} \\\alpha\end{bmatrix}}$

[0059] on the basis of the first effective operation term T2, secondeffective operation term T4 and third effective operation term T5calculated by the operation term calculation means, the minimum value αcalculated by the maximum value/minimum value calculation means and thecoefficient matrix Uij calculated by the coefficient generation means,thereby calculating the first color correction amounts R1, G1, B1.

[0060] In a thirteenth aspect of a color correcting method according tothe present invention, a color converting method which carries out colorcorrection on first color data to convert to second color datacorresponding to the first color data, includes the steps of: (a)calculating a first color correction amount on the basis of the firstcolor data by using a matrix computing system; (b) calculating amultiplication coefficient on the basis of characteristic information ofthe first color data; (c) calculating a second color correction amountby multiplying the first color collection amount by the multiplicationcoefficient; and (d) calculating the second color data by adding thesecond color correction amount to the first color data.

[0061] In a fourteenth aspect of the color correcting method accordingto the present invention, the characteristic information of the firstcolor data is brightness.

[0062] In a fifteenth aspect of the color correcting method according tothe present invention, the value of the multiplication coefficientcalculated in the step (b) becomes smaller as the brightness becomessmaller than a predetermined value.

[0063] In a sixteenth aspect of the color correcting method according tothe present invention, the value of the multiplication coefficientcalculated in the step (b) becomes smaller as the brightness becomeslarger than a predetermined value.

[0064] In a seventeenth aspect of the color correcting method accordingto the present invention, the characteristic information of the firstcolor data is saturation.

[0065] In an eighteenth aspect of the color correcting method accordingto the present invention, the value of the multiplication coefficientcalculated in the step (b) becomes smaller as the saturation becomeslarger than a predetermined value.

[0066] In a nineteenth aspect of the color correcting method accordingto the present invention, the color converting method further includesthe step of: (e) calculating the characteristic information on the basisof the first color data.

[0067] In a twentieth aspect of the color correcting method according tothe present invention, the characteristic information calculated in thestep (e) is brightness of the first color data, and the brightness iscalculated as a sum of values obtained by multiplying the respectivecomponents of the first color data by predetermined coefficients.

[0068] In a twenty-first aspect of the color correcting method accordingto the present invention, the characteristic information calculated inthe step (e) is brightness of the first color data, and the brightnessis calculated as the maximum value of the components of the first colordata.

[0069] In a twenty-second aspect of the color correcting methodaccording to the present invention, the characteristic informationcalculated in the step (e) is saturation of the first color data, andthe saturation is calculated on the basis of a difference between themaximum value of the components of the first color data and the minimumvalue of the components of the first color data.

[0070] In a twenty-third aspect of the color correcting method accordingto the present invention, the first color data and the first colorcorrection amounts are respectively Ri, Gi, Bi and R1, G1, B1corresponding to three primary color signals of red, green and blue, andthe step (c) includes the steps of: (f) calculating the minimum value αand the maximum value β of the first color data; (g) calculating six huedata: r=Ri−α, g=Gi−α, b=Bi−α, y=β−Ri, m=β−Gi and c=β−Ri, respectivelyrelating to red, green, blue, yellow, magenta and cyan, from the firstcolor data and the minimum value α and maximum value β calculated in thestep (f); (h) calculating, by using the hue data calculated in the step(g) and a predetermined coefficients ap1 to ap6 and aq1 to aq6, a firsteffective operation term T2 having only a value which is not zero amongh1r=MIN (y, m), h1g=MIN (c, y) and h1b=MIN (m, c) or a zero value whenall the h1r, h1g and h1b are zero, a second effective operation term T4having only a value which is not zero among h1y=MIN (r, g), h1c=MIN (g,b) and h1m=MIN (b, r) or a zero value when all the h1y, h1c and h1m arezero, and a third effective operation term T5 having only a value whichis not zero among h2ry=MW (aq1×h1y, ap1×h1r), h2rm=MIN (aq2×h1m,ap2×h1r), h2gy=MIN (aq3×h1y, ap3×h1g), h2gc=MIN (aq4×h1c, ap4×h1g),h2bm=MIN (aq5×h1m, ap5×h1b) and h2bc=MIN (aq6×h1c, ap6×h1b) or a zerovalue when all the h2ry, h2rm, h2gy, h2gc, h2bm and h2bc are zero; (i)calculating a coefficient matrix Uij on the basis of the α and βcalculated in the step (f); and (j) carrying out the following matrixoperation: $\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {\left( {U\quad i\quad j} \right)\begin{bmatrix}{T2} \\{T4} \\{T5} \\\alpha\end{bmatrix}}$

[0071] on the basis of the first effective operation term T2, secondeffective operation term T4 and third effective operation term T5calculated in the step (h), the minimum value α calculated in the step(f) and the coefficient matrix Uij calculated in the step (i), therebycalculating the first color correction amounts R1, G1, B1.

[0072] In a first aspect of a semiconductor device according to thepresent invention, since the color converter includes: first colorcorrection amount calculation means for calculating a first colorcorrection amount on the basis of the first color data by using a matrixcomputing system; multiplication coefficient calculation means forcalculating a multiplication coefficient on the basis of characteristicinformation of the first color data; second color correction amountcalculation means for calculating a second color correction amount bymultiplying the first color collection amount by the multiplicationcoefficient; and color correction amount addition means for calculatingthe second color data by adding the second color correction amount tothe first color data, it is possible to determine the degree of theinfluence of noise components in the first color data and thepossibility of occurrence of damaged color due to the color conversionprocess on the basis of the characteristic information of the firstcolor data. Consequently, when the inputted first color data areseriously susceptible to the noise components and when damaged colortends to occur in the color conversion process, the multiplicationcoefficient is set to a low level so that it is possible to solve theproblem of emphasized influences of noise components and the problem ofthe occurrence of damaged color due to the color conversion process forenhancing the saturation, which have been caused by the color converterusing the conventional matrix operation system.

[0073] Moreover, since the calculation of the first color correctionamount is performed by using the matrix operation system, it is notnecessary to use large capacity memories such as those required for thetable conversion system. Therefore, it is possible to solve the problemof difficulty in applying LSIs and the problem of difficulty in flexiblychanging conversion characteristics, which have been caused by the colorconverter using the conventional table conversion system.

[0074] In the second aspect of the color correcting device according tothe present invention, the characteristic information of the first colordata is brightness. Therefore, on the basis of the degree of brightness,it is possible to determine the degree of influences of noise componentsto the first color data and the possibility of generation of damagedcolor due to the color conversion process. Consequently, when theinputted first color data are seriously susceptible to the noisecomponents and when damaged color tends to occur in the color conversionprocess, the multiplication coefficient is set to a low level so that itis possible to solve the problem of emphasized influences of noisecomponents and the problem of the occurrence of damaged color due to thecolor conversion process for enhancing the saturation, which have beencaused by the color converter using the conventional matrix operationsystem.

[0075] In the third aspect of the color correcting device of the presentinvention, the value of the multiplication coefficient calculated by themultiplication coefficient calculation means becomes smaller as thebrightness becomes smaller than a predetermined value. Therefore, it ispossible to reduce emphasized influences of noise components due to thecolor conversion process for enhancing the saturation in the case wherethe component of the first color data is small and seriously susceptibleto the influences of noise components.

[0076] In the fourth aspect of the color correcting device according tothe present invention, the value of the multiplication coefficientcalculated by the multiplication coefficient calculation means becomessmaller as the brightness becomes larger than a predetermined value.Therefore, it is possible to reduce the generation of damaged color dueto the color conversion process for enhancing the saturation, in thecase where the brightness of the first color data is high and damagedcolor tends to occur.

[0077] In the fifth aspect of the color correcting device according tothe present invention, the characteristic information of the first colordata is saturation. Therefore, on the basis of the degree of saturation,it is possible to determine the possibility of generation of damagedcolor due to the color conversion process in the first color data.Consequently, when the inputted first color data are seriouslysusceptible to the noise components and when damaged color tends tooccur in the color conversion process, the multiplication coefficient isset to a low level so that it becomes possible to solve the problem ofemphasized influences of noise components and the problem of theoccurrence of damaged color due to the color conversion process forenhancing the saturation, which have been caused by the color converterusing the conventional matrix operation system.

[0078] In the sixth aspect of the color correcting device according tothe present invention, the value of the multiplication coefficientcalculated by the multiplication coefficient calculation means becomessmaller as the saturation becomes higher than a predetermined value.Therefore, it is possible to reduce the generation of damaged color dueto the color conversion process for enhancing the saturation, in thecase where the saturation of the first color data is high and damagedcolor tends to occur.

[0079] In the seventh aspect of the color correcting device according tothe present invention, the color converter further includescharacteristic information calculation means for calculating thecharacteristic information on the basis of the first color data.Therefore, the color correcting device is allowed to properly deal witha case where no characteristic information is externally inputted sothat it needs to be calculated from the first color data.

[0080] In the eighth aspect of the color correcting device according tothe present invention, the characteristic information calculated by thecharacteristic information calculation means is brightness of the firstcolor data, and the brightness is calculated as a sum of values obtainedby multiplying the respective components of the first color data bypredetermined coefficients. Therefore, for example, by setting thecoefficient by which each of the components of the first color data ismultiplied to a value which is suitable for human visual sensationcharacteristics, it is possible to calculate and find brightnessinformation that is close to human sensitivity. Moreover, in an attemptto find brightness information on the basis of the standard such as NTSCand sRGB or the standard color space, it is possible to easily obtainthe information by altering the coefficient.

[0081] In the ninth aspect of the color correcting device according tothe present invention, the characteristic information calculated by thecharacteristic information calculation means is brightness of the firstcolor data, and the brightness is calculated as the maximum value of thecomponents of the first color data. Therefore, it is not necessary tocarry out a multiplying process so as to calculate the brightness, andit becomes possible to reduce the operation load imposed on thecharacteristic information calculation means, and also to reduce thecircuit scale in the hardware configuration.

[0082] In the tenth aspect of the color correcting device according tothe present invention, the characteristic information calculated by thecharacteristic information calculation means is saturation of the firstcolor data, and the saturation is calculated on the basis of adifference between the maximum value of the components of the firstcolor data and the minimum value of the components of the first colordata. Therefore, the saturation is easily calculated by using themaximum value and the minimum value that are found by a smallercalculation load so that it becomes possible to reduce the operationload imposed on the characteristic information calculation means, andalso to reduce the circuit scale in the hardware configuration.Moreover, the saturation is calculated as a difference between themaximum value of the components of the first data and the minimum valueof the components of the first data so that the saturation is calculatedby using only the subtracting process. Thus, it becomes possible tofurther improve the effects.

[0083] In the eleventh aspect of the color correcting device accordingto the present invention, the multiplication coefficient calculationmeans includes a look up table storing the multiplication coefficientcorresponding to the characteristic information. Therefore, by rewritingthe contents of the table, it becomes possible to easily achieve variouscharacteristics without altering the circuit configuration.

[0084] Here, the look up table which is required for the multiplicationcoefficient calculation means in the present invention is achieved by aone-dimensional look up table associated with only the characteristicinformation of the first color data. In other words, it is not necessaryto provide a large capacity look up table such as a three-dimensionallook up table used in the conventional table conversion system.

[0085] In the twelfth aspect of the color correcting device according tothe present invention, the first color data and the first colorcorrection amounts are respectively Ri, Gi, Bi and R1, G1, B1corresponding to three primary color signals of red, green and blue, andthe first color correction calculation means includes: maximumvalue/minimum value calculation means for calculating the minimum valueα and the maximum value β of the first color data; hue data calculationmeans for calculating six hue data: r=Ri−α, g=Gi−α, b=Bi−α, y=β−Ri,m=β−Gi and c=β−Ri, respectively relating to red, green, blue, yellow,magenta and cyan, from the first color data and the minimum value α andmaximum value β calculated by the maximum value/minimum valuecalculation means; effective operation term calculation means (18) forcalculating, by using the hue data and a predetermined coefficients ap1to ap6 and aq1 to aq6, a first effective operation term T2 having only avalue which is not zero among h1r=MIN (y, m), h1g=MIN (c, y) and h1b=MIN(m, c) or a zero value when all the h1r, h1g and h1b are zero, a secondeffective operation term T4 having only a value which is not zero amongh1y=MIN (r, g), h1c=MIN (g, b) and h1m=MIN (b, r) or a zero value whenall the h1y, h1c and h1m are zero, and a third effective operation termT5 having only a value which is not zero among h2ry=MS (aq1×h1y,ap1×h1r), h2rm=MIN (aq2×h1m, ap2×h1r), h2gy=MIN (aq3×h1y, ap3×h1g),h2gc=MIN (aq4×h1c, ap4×h1g), h2bm=MIN (aq5×h1m, ap5×h1b) and h2bc=MIN(aq6×h1c, ap6×h1b) or a zero value when all the h2ry, h2rm, h2gy, h2gc,h2bm and h2bc are zero; coefficient generation means for calculating acoefficient matrix Uij on the basis of the minimum value α and maximumvalue β calculated by the maximum value/minimum value calculation means;and matrix operation means for carrying out the following matrixoperation: $\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {\left( {U\quad i\quad j} \right)\begin{bmatrix}{T2} \\{T4} \\{T5} \\\alpha\end{bmatrix}}$

[0086] on the basis of the first effective operation term T2, secondeffective operation term T4 and third effective operation term T5calculated by the operation term calculation means, the minimum value αcalculated by the maximum value/minimum value calculation means and thecoefficient matrix Uij calculated by the coefficient generation means,thereby calculating the first color correction amounts R1, G1, B1.Therefore, it is possible to carry out a correction process on only atarget hue or a predetermined area between hues in an independentmanner, and also to correct the degree of a change in the area betweenhues in an independent manner. In other words, it is possible toflexibly change conversion characteristics.

[0087] Moreover, the matrix operation, which is originally carried outon the basis of the above-mentioned thirteen polynomial data: h1r, h1g,h1b, h1y, h1c, h1m, h2ry, h2gy, h2gc, h2bc, h2bm, h2rm and α, can becarried out by using four effective polynomial data: the first effectiveoperation term T2, the second effective operation term T4, the thirdeffective operation term T5 and the minimum value α. Consequently, itbecomes possible to greatly reduce the operation load to be imposed onthe first color correction amount calculation means, and particularly toreduce the circuit scale greatly in the case of a hardwareconfiguration.

[0088] In the thirteenth aspect of the color correcting method of thepresent invention, a color converting method which carries out colorcorrection on first color data to convert to second color datacorresponding to the first color data, includes the steps of: (a)calculating a first color correction amount on the basis of the firstcolor data by using a matrix computing system; (b) calculating amultiplication coefficient on the basis of characteristic information ofthe first color data; (c) calculating a second color correction amountby multiplying the first color collection amount by the multiplicationcoefficient; and (d) calculating the second color data by adding thesecond color correction amount to the first color data. Therefore, it ispossible to determine the degree of influences of noise components tothe first color data and the possibility of generation of damaged colordue to the color conversion process on the basis of the characteristicinformation of the first color data. Consequently, when the inputtedfirst color data are seriously susceptible to the noise components andwhen damaged color tends to occur in the color conversion process, themultiplication coefficient is set to a low level so that it becomespossible to solve the problem of emphasized influences of noisecomponents and the problem of the occurrence of damaged color due to thecolor conversion process for enhancing the saturation, which have beencaused by the color converter using the conventional matrix operationsystem.

[0089] Moreover, since the first color correction amount is calculatedby using the matrix operation system, it is not necessary to use largecapacity memories such as those required for the table conversionsystem. Therefore, it is possible to solve the problem of difficulty inapplying LSIs and the problem of difficulty in flexibly changingconversion characteristics, which have been caused by the colorconverter using the conventional table conversion system.

[0090] In the fourteenth aspect of the color correcting method accordingto the present invention, the characteristic information of the firstcolor data is brightness. Therefore, on the basis of the degree ofbrightness, it is possible to determine the degree of influences ofnoise components to the first color data and the possibility ofgeneration of damaged color due to the color conversion process.Consequently, when the inputted first color data are seriouslysusceptible to the noise components and when damaged color tends tooccur in the color conversion process, the multiplication coefficient isset to a low level so that it becomes possible to solve the problem ofemphasized influences of noise components and the problem of theoccurrence of damaged color due to the color conversion process forenhancing the saturation, which have been caused by the color convertingmethod using the conventional matrix operation system.

[0091] In the fifteenth aspect of the color correcting method accordingto the present invention, the value of the multiplication coefficientcalculated in the step (b) becomes smaller as the brightness becomessmaller than a predetermined value. Therefore, it is possible to reduceemphasized influences of noise components due to the color conversionprocess for enhancing the saturation in the case where the component ofthe first color data is small and seriously susceptible to theinfluences of noise components.

[0092] In the sixteenth aspect of the color correcting method accordingto the present invention, the value of the multiplication coefficientcalculated in the step (b) becomes smaller as the brightness becomeslarger than a predetermined value. Therefore, it is possible to reducethe generation of damaged color due to the color conversion process forenhancing the saturation, in the case where the brightness of the firstcolor data is high and damaged color tends to occur.

[0093] In the seventeenth aspect of the color correcting methodaccording to the present invention, the characteristic information ofthe first color data is saturation. Therefore, on the basis of thedegree of saturation, it is possible to determine the possibility ofgeneration of damaged color due to the color conversion process in thefirst color data. Consequently, when the inputted first color data areseriously susceptible to the noise components and when damaged colortends to occur in the color conversion process, the multiplicationcoefficient is set to a low level so that it becomes possible to solvethe problem of emphasized influences of noise components and the problemof the occurrence of damaged color due to the color conversion processfor enhancing the saturation, which have been caused by the colorconverting method using the conventional matrix operation system.

[0094] In the eighteenth aspect of the color correcting method accordingto the present invention, the value of the multiplication coefficientcalculated in the step (b) becomes smaller as the saturation becomeslarger than a predetermined value. Therefore, it is possible to reducethe generation of damaged color due to the color conversion process forenhancing the saturation, in the case where the saturation of the firstcolor data is high and damaged color tends to occur.

[0095] In the nineteenth aspect of the color correcting method accordingto the present invention, the color converting method further includesthe step of: (e) calculating the characteristic information on the basisof the first color data. Therefore, the color correcting method isallowed to properly deal with a case where no characteristic informationis externally inputted so that it needs to be calculated from the firstcolor data.

[0096] In the twentieth aspect of the color correcting method accordingto the present invention, the characteristic information calculated inthe step (e) is brightness of the first color data, and the brightnessis calculated as a sum of values obtained by multiplying the respectivecomponents of the first color data by predetermined coefficients.Therefore, for example, by setting the coefficient by which each of thecomponents of the first color data is multiplied to a value which issuitable for human visual sensation characteristics, it is possible tocalculate and find brightness information that is close to humansensitivity. Moreover, in an attempt to find brightness information onthe basis of the standard such as NTSC and sRGB or the standard colorspace, it is possible to easily obtain the information by altering thecoefficient.

[0097] In the twenty-first aspect of the color correcting methodaccording to the present invention, the characteristic informationcalculated in the step (e), is brightness of the color data, and thebrightness is calculated as the maximum value of the components of thefirst color data. Therefore, it is not necessary to carry out amultiplying process so as to calculate the brightness, and it becomespossible to reduce the operation load imposed on the characteristicinformation calculation means, and also to reduce the circuit scale inthe hardware configuration.

[0098] In the twenty-second aspect of the color correcting method of thepresent invention, the characteristic information calculated in the step(e) is saturation of the first color data, and the saturation iscalculated on the basis of a difference between the maximum value of thecomponents of the first color data and the minimum value of thecomponents of the first color data. Therefore, the calculation of thesaturation is easily carried out by using the maximum value and theminimum value that are found by a smaller calculation load so that itbecomes possible to reduce the operation load imposed on thecharacteristic information calculation means, and also to reduce thecircuit scale in the hardware configuration. Moreover, the saturation iscalculated as a difference between the maximum value of the componentsof the first data and the minimum value of the components of the firstdata so that the saturation is calculated by using only the subtractingprocess; thus, it becomes possible to further improve the effects.

[0099] In the twenty-third aspect of the color correcting method of thepresent invention, the first color data and the first color correctionamounts are respectively Ri, Gi, Bi and R1, G1, B1 corresponding tothree primary color signals of red, green and blue, and the step (c)includes the steps of: (f) calculating the minimum value α and themaximum value β of the first color data; (g) calculating six hue data:r=Ri−α, g=Gi−α, b=Bi−α, y=β−Ri, m=β−Gi and c=β−Ri, respectively relatingto red, green, blue, yellow, magenta and cyan, from the first color dataand the minimum value α and maximum value β calculated in the step (f);(h) calculating, by using the hue data calculated in the step (g) and apredetermined coefficients ap1 to ap6 and aq1 to aq6, a first effectiveoperation term T2 having only a value which is not zero among h1r=MIN(y, m), h1g=MIN (c, y) and h1b=MIN (m, c) or a zero value when all theh1r, h1g and h1b are zero, a second effective operation term T4 havingonly a value which is not zero among h1y=MIN (r, g), h1c=MIN (g, b) andh1m=MIN (b, r) or a zero value when all the h1y, h1c and h1m are zero,and a third effective operation term T5 having only a value which is notzero among h2ry=MIN (aq1×h1y, ap1×h1r), h2rm=MIN (aq2×h1m, ap2×h1r),h2gy=MIN (aq3×h1y, ap3×h1g), h2gc=MIN (aq4×h1c, ap4×h1g), h2bm=MIN(aq5×h1m, ap5×h1b) and h2bc=MIN (aq6×h1c, ap6×h1b) or a zero value whenall the h2ry, h2rm, h2gy, h2gc, h2bm and h2bc are zero; (i) calculatinga coefficient matrix Uij on the basis of the α and β calculated in thestep (f); and (j) carrying out the following matrix operation:$\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {\left( {U\quad i\quad j} \right)\begin{bmatrix}{T2} \\{T4} \\{T5} \\\alpha\end{bmatrix}}$

[0100] on the basis of the first effective operation term T2, secondeffective operation term T4 and third effective operation term T5calculated in the step (h), the minimum value α calculated in the step(f) and the coefficient matrix Uij calculated in the step (i), therebycalculating the first color correction amounts R1, G1, B1. Therefore, itis possible to carry out a correction process on only a target hue or apredetermined area between hues in an independent manner, and also tocorrect the degree of a change in the area between hues in anindependent manner. In other words, it is possible to flexibly changeconversion characteristics.

[0101] Moreover, the matrix operation, which is originally carried outon the basis of the above-mentioned thirteen polynomial data: h1r, h1g,h1b, h1y, h1c, h1m, h2ry, h2gy, h2gc, h2bc, h2bm, h2rm and α, can becarried out by using four effective polynomial data: the first effectiveoperation term T2, the second effective operation term T4, the thirdeffective operation term T5 and the minimum value α. Consequently, itbecomes possible to greatly reduce the operation load to be imposed onthe first color correction amount calculation means, and particularly toreduce the circuit scale greatly in the case of a hardwareconfiguration.

[0102] These and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0103]FIG. 1 is a block diagram showing one example of a configurationof a color converter according to embodiment 1;

[0104]FIG. 2 is a block diagram showing one example of a configurationof first color correction amount calculation means in the colorconverter according to embodiment 1;

[0105]FIG. 3 is a block diagram showing one example of a configurationof multiplication coefficient calculation means in the color converteraccording to embodiment 1;

[0106]FIG. 4 is a block diagram showing one example of a configurationof brightness information calculation means in the color converteraccording to embodiment 1;

[0107]FIG. 5 is a graph showing one example of the relationship betweenmultiplication coefficient k and brightness information V to be storedin a look up table in the color converter according to embodiment 1;

[0108]FIG. 6 is a graph showing one example of the relationship betweenmultiplication coefficient k and brightness information V to be storedin a look up table in the color converter according to embodiment 1;

[0109]FIG. 7 is a block diagram showing one example of a configurationof a color converter according to embodiment 2;

[0110]FIG. 8 is a block diagram showing one example of a configurationof brightness information calculation means in a color converteraccording to embodiment 3;

[0111]FIG. 9 is a graph showing one example of the relationship betweenmultiplication coefficient k and brightness information V to be storedin a look up table in a color converter according to embodiment 4;

[0112]FIG. 10 is a block diagram showing one example of a configurationof multiplication coefficient calculation means in a color converteraccording to embodiment 5;

[0113]FIG. 11 is a block diagram showing one example of a configurationof saturation information calculation means in the color converteraccording to embodiment 5;

[0114]FIG. 12 is a graph showing one example of the relationship betweenmultiplication coefficient k and saturation information SA to be storedin a look up table in the color converter according to embodiment 5;

[0115]FIG. 13 is a graph showing one example of the relationship betweenmultiplication coefficient k and saturation information SA to be storedin a look up table in the color converter according to embodiment 5;

[0116] FIGS. 14(A) to 14(F) are schematic diagrams showing therelationship between hue data r, g, b, y, m, c and six hues inembodiment 6;

[0117] FIGS. 15(A) to 15(F) are schematic diagrams showing therelationship between first operation terms h1r, h1y, h1g, h1c, h1b, h1mand six hues in embodiment 6;

[0118] FIGS. 16(A) to 16(F) are schematic diagrams showing therelationship between second operation terms and six hues, in the casewhere the values of operation coefficients aq1 to aq6 and ap1 to ap6 inthe second operation terms hry, hrm, hgy, hgc, hbm, hbc are all set to1, in embodiment 6;

[0119] FIGS. 17(A) to 17(F) are schematic diagrams showing therelationship between second operation terms and six hues, in the casewhere the values of operation coefficients aq1 to aq6 and ap1 to ap6 inthe second operation terms hry, hrm, hgy, hgc, hbm, hbc are varied, inembodiment 6;

[0120] FIGS. 18(a) and 18(b) are tables showing the correspondingrelationship between six hues and areas between the hues and effectiveoperation terms associated therewith in embodiment 6;

[0121]FIG. 19 is a block diagram showing one example of a configurationof first color correction amount calculation means in a color converteraccording to embodiment 6;

[0122]FIG. 20 is a block diagram showing one example of a configurationof a polynomial computing unit in the color converter according toembodiment 6;

[0123]FIG. 21 is a diagram showing the corresponding relationship amongthe value of identification code S1, the maximum value β and the minimumvalue α and hue data that are set to zero in the first color data, inembodiment 6;

[0124]FIG. 22 is a table for describing the operation of azero-eliminating device in the color converter according to embodiment6;

[0125]FIG. 23 is a block diagram showing a part of a configuration of amatrix computing unit in the color converter according to embodiment 6;

[0126] FIGS. 24(a) to 24(c) are graphs showing one example of theoriginal color data components and noise components and color datacomponents to be inputted to an image display device, in the case wherethe noise components are smaller than the original color data;

[0127] FIGS. 25(a) to 25(c) are graphs showing one example of theoriginal color data components and noise components, and color datacomponents to be inputted to an image display device, in the case wherethe noise components are greater than the original color data; and

[0128]FIG. 26 is a block diagram showing a configuration of a colorconverter in a conventional matrix computing system.

BEST MODES FOR CARRYING OUT THE INVENTION 1. Embodiment 1

[0129]FIG. 1 is a block diagram showing one example of a configurationof a color converter according to embodiment 1. In this Figure,reference numeral 1 is first color correction amount calculation means,2 is color correction amount addition means, 4 is multiplicationcoefficient calculation means, and 5 is second color-correctioncalculation means. The configuration of the first color correctionamount calculation means 1 will be described later, and the first colorcorrection amount calculation means 1 and the color correction amountaddition means 2 may have the same configurations as color correctionamount calculation means 101 and color correction amount addition means102 in a conventional color converter, respectively shown in FIG. 26.

[0130] First color data Ri, Gi, Bi, which are targets forcolor-conversion processes, are inputted to the first color correctionamount calculation means 1, the color correction amount addition means 2and the multiplication coefficient calculation means 4. In the firstcolor correction amount calculation means 1, first color correctionamounts R1, G1, B1 that correspond to the first color data Ri, Gi, Biare calculated by linear operations shown in the following equation (9),and inputted to the second color correction amount calculation means 5.$\begin{matrix}{\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {\left( {A\quad 1i\quad j} \right)\begin{bmatrix}{R\quad i} \\{G\quad i} \\{B\quad i}\end{bmatrix}}} & {{Equation}\quad (9)}\end{matrix}$

[0131] In this equation, A1ij represents a coefficient matrix in whichi=1 to 3 and j=1 to 3.

[0132] Moreover, in the multiplication coefficient calculation means 4,a multiplication coefficient k is calculated from the first color dataRi, Gi, Bi, and outputted to the second color correction amountcalculation means 5. Then, in the second color correction amountcalculation means 5, the first color correction amounts R1, G1, B1 arerespectively multiplied by the multiplication coefficient k so that thesecond color correction amounts R2, G2, B2 are found, and these areoutputted to the color correction amount addition means 2. The colorcorrection amount addition means 2 adds the first color data Ri, Gi, Biand the second color correction amounts R2, G2, B2 so as to find thesecond color data Ro, Go, Bo, which are output data after the colorconversion. In other words, the second color data Ro, Go, Bo, outputtedfrom the color correction amount addition means 2, are represented bythe following equation (10). $\begin{matrix}{\begin{bmatrix}{Ro} \\{Go} \\{Bo}\end{bmatrix} = {\begin{bmatrix}{Ri} \\{Gi} \\{Bi}\end{bmatrix} + {k\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix}}}} & {{Equation}\quad (10)}\end{matrix}$

[0133] Moreover, FIG. 2 is a block diagram showing a structural exampleof the first color correction amount calculation means 1 shown inFIG. 1. In this Figure, reference numeral 6 a is a matrix computing unitand 7 a is a coefficient generator. The coefficient generator 7 agenerates a coefficient A1ij for matrix operations in equation (9), andsends this to the matrix computing unit 6 a. The matrix computing unit 6a calculates equation (9) by using the first color data Ri, Gi, Bi andthe coefficient A1ij from the coefficient generator 7 a to find thefirst color-correction data R1, G1, B1. Here, it is clear that theoperation of equation (9) is easily achieved by multiplication means andaddition means; therefore, the detailed description thereof will not berepeated.

[0134] Moreover, FIG. 3 is a block diagram showing a structural exampleof the multiplication coefficient calculation means 4 shown in FIG. 1.In this Figure, reference numeral 8 is brightness informationcalculation means, and 9 is a look up table (LUT). The first color dataRi, Gi, Bi, inputted to the multiplication coefficient calculation means4, are inputted to the brightness information calculation means 8. Thebrightness information calculation means 8 calculates brightnessinformation V that is information for indicating brightness of the firstcolor data, and outputs this to a look up table 9.

[0135] The look up table 9, which is constituted by a memory, etc.,preliminarily stores values of the multiplication coefficient thatcorrespond to values of the brightness information V. The look up table9 extracts the multiplication coefficient k corresponding to theinputted value of brightness information V from a memory, and outputsthe resulting value. For example, values of the multiplicationcoefficient k that respectively correspond to values of the brightnessinformation V are preliminarily stored in the memory of the look uptable 9 with the brightness information V being set in the form ofaddresses; thus, by inputting brightness information V as a readoutaddress, the corresponding multiplication coefficient k can beoutputted.

[0136] Here, FIG. 4 is a block diagram showing a structural example ofthe brightness information calculation means 8 shown in FIG. 1. In thisFigure, reference numerals 10 a, 10 b, 10 c are multipliers, and 11 aand 11 b are adders. The first color data Ri, Gi, Bi are inputted to therespective multipliers 10 a, 10 b, 10 c together with predeterminedcoefficients kr, kg, kb, and the respective results of multiplicationare outputted. The outputs from the multipliers 10 b and 10 c areinputted to the adder 11 a, and the results of the addition areoutputted. The output of the adder 11 a is further inputted to the adder11 b together with the output of the multiplier 10 a so that the resultof the addition is outputted as brightness information V. In otherwords, in the brightness information calculation means 8 shown in FIG.4, the brightness information V of the first color data is representedby the following equation (11).

V=kr×Ri+kg×Gi+kb×Bi   Equation (11)

[0137] For example, in the case where the first color data Ri, Gi, Biare color data in compliance with NTSC, kr=0.3, kg=0.59 and kb=0.11 areset in equation (11). Moreover, for example, supposing that kr=0.25,kg=0.5 and kb=0.25, the multipliers 10 a, 10 b, 10 c may be achieved bybit shifts so that it is possible to downsize the circuit configuration.

[0138] Here, the following description will discuss the relationshipbetween the brightness information V and the multiplication coefficientk outputted from the look up table 9. In the following description, itis assumed that the first color data Ri, Gi, Bi are integers from 0 to255. Moreover, it is also assumed that the brightness information V isindicated by an integer from 0 to 255, and found from equation (11) withsettings of kr=0.25, kg=0.5 and kb=0.25. Moreover, it is assumed thatthe multiplication coefficient k is given as a decimal fraction from notless than 0 to not more than 1.

[0139] As described above, in the case where the original color datacomponents Rs, Gs, Bs in a dark portion and the like of an image aresmall, that is, in the case where the brightness of the color data islow, the color data are seriously susceptible to influences of noisecomponents. Therefore, in such a case, when the color conversion processfor enhancing the saturation of the color data is carried out, that is,when the process for emphasizing the color is carried out, theinfluences of noise components are further emphasized, with the resultthat, instead of improving the image, the color-conversion processcauses a defective image to be displayed on an image display device.Moreover, when the original color data components Rs, Gs, Bs are small,the first color data Ri, Gi, Bi to be inputted to the device also becomesmaller. Therefore, in the present embodiment, it is possible to reducethe correction amount of color conversion for enhancing the saturationof the color data to a small level, when the brightness of the firstcolor data is low (that is, when the brightness of the original colordata is low).

[0140]FIG. 5 is a graph that indicates one example of the relationshipbetween the multiplication coefficient k and brightness information V tobe stored in the look up table 9. When V=0, k=0, and when V=255, k=1,and in this range, the value of the multiplication coefficient k islinearly varied with respect to the brightness information V.

[0141] In the case where the relationship between the multiplicationcoefficient k and the brightness information V to be stored in the lookup table 9 is shown in the graph of FIG. 5, in an example shown in FIG.24 in which the original color data are Rs=192, Gs=64, Bs=64 with noisecomponents being set to Rn=8, Gn=8, Bn=24, the first color data arerepresented by Ri=200, Gi=72, Bi=88. In contrast to the original colorcomponents Rs, Gs, Bs which exhibit a red color, the first color dataRi, Gi, Bi exhibit a slightly bluish red color due to the influences ofthe noise components Rn, Gn, Bn. At this time, the brightnessinformation of the first color data obtained from equation (11) isV=108, with the multiplication coefficient k=0.42 obtained from therelationship of FIG. 5.

[0142] In an example shown in FIG. 25, in which the color data areRs=24, Gs=8, Bs=8 with noise components being set to Rn=8, Gn=8, Bn=24,the first color data are represented by Ri=32, Gi=16, Bi=32. In contrastto the original color components Rs, Gs, Bs which exhibit a red color,the first color data Ri, Gi, Bi exhibit a magenta color due to theinfluences of the noise components Rn, Gn, Bn, resulting in a greatchange in hues. At this time, the brightness information data is V=24,with the multiplication coefficient being set to k=0.09 from therelationship of FIG. 5.

[0143] In the second color correction amount calculation means 5, thefirst color correction amounts R1, G1, B1 are respectively multiplied bythe multiplication coefficient k so that the second color correctionamounts R2, G2, B2, which form final correction amounts, are calculatedand obtained. Therefore, as the multiplication coefficient k becomessmaller, the correction amount by the color conversion process isreduced. Moreover, since the relationship between the multiplicationcoefficient k and the brightness information V is set as shown in FIG.5, the multiplication coefficient k becomes smaller as the brightness ofthe first color data is reduced, as shown in the above-mentionednumerical example.

[0144] As a result, in the case where the brightness of the originalcolor data is small, and seriously susceptible to influences of noisecomponents, the correction amount by the color conversion process isreduced to a small level. In contrast, in the case where the brightnessof the original color data is great, and less susceptible to influencesof noise components, the color conversion process for emphasizing thecolor is carried out in a level close to the conventional level byincreasing the multiplication coefficient k.

[0145] Therefore, it becomes possible to solve the problem of emphasizedinfluences of noise components with respect to color data having lowbrightness due to the color conversion process for enhancing thesaturation thereof, which have been caused by the color converter usingthe conventional matrix operation system.

[0146] Moreover, in this case, a look up table is used as the means forfinding the multiplication coefficient k from the brightness informationV; however, the look up table to be used here is achieved by aone-dimensional table with respect to the brightness information V. Inother words, it is not necessary to provide a large capacity look uptable such as a three-dimensional look up table with respect to colordata R, G, B used in the conventional table conversion system.

[0147] Therefore, it is possible to solve the problem of difficulty inapplying LSIs and the problem of difficulty in flexibly changingconversion characteristics due to the necessity of a large capacitymemory, which have been caused by the color converter using theconventional table conversion system.

[0148] In FIG. 5, the relationship between the brightness information Vand the multiplication coefficient k is a proportional relationship;however, in the present embodiment, the relationship of the two elementsis not limited to this relationship, and any relationship which makesthe multiplication coefficient k small when the value of the brightnessinformation V is small may be used with the same effects.

[0149] For example, FIG. 6 is a graph that shows another example of therelationship between the multiplication coefficient k and the brightnessinformation V to be stored in the look up table 9. In the case where thebrightness of the first color data is low and seriously susceptible tothe influences of noise components (in the case of brightnessinformation V<30), the multiplication coefficient k=0 is set so that nocolor emphasizing process is carried out in the color-conversionprocess. In contrast, in the case where the brightness of the firstcolor data is high, and less susceptible to the influences of noisecomponents (in the case of brightness information V>122), the value ofthe multiplication coefficient k is set to 1, and the color emphasizingprocess is carried out by the color-conversion process in the samemanner as the conventional process. Moreover, in the range of brightnessinformation 30<V<122, as shown in the same Figure, the value of themultiplication coefficient k is linearly varied with respect to thebrightness information V.

[0150] Here, in the case of the first color data, Ri=200, Gi=72, Bi=88,the brightness information V=108 and the multiplication coefficientk=0.85 so that the relationship between the multiplication coefficient kand the brightness information V allows the color emphasizing operationby the color-conversion process to be more effectively carried out incomparison with the case shown in FIG. 5. Moreover, in the case ofRi=32, Gi=16, Bi=32, the brightness information V=24 and themultiplication coefficient k=0 so that no color emphasizing process iscarried out.

[0151] In other words, in the case of the relationship of the brightnessinformation V and the multiplication coefficient k shown in FIG. 5, itis possible to reduce the influences of noise components generally froma small level to a great level of the brightness information V; however,the effects of emphasizing the saturation becomes smaller as a whole. Incontrast, in the case of FIG. 6, when the brightness information V issmall, the effects of reducing the noise components are particularlyexerted greatly, and when the brightness information is great, theeffects of emphasizing the saturation are exerted greatly.

[0152] Moreover, in the present embodiment, the look up table is used asthe means for finding the corresponding multiplication coefficient kfrom the brightness information V; however, this means may be formed byusing arithmetic circuits and the like. However, the arrangement usingthe look up table has an advantage that is not achieved by arithmeticcircuits, in that various characteristics are easily achieved byrewriting the contents of the table without changing the circuitconfiguration.

[0153] As described above, in accordance with the color converter andcolor converting method according to the present embodiment, in the casewhere the process for enhancing the saturation of color data is carriedout, without the necessity of using any large capacity memory, it ispossible to achieve superior color reproduction without furtheremphasizing the influences of noise components even in color data thathave low brightness and tend to have adverse effects from the noisecomponents.

[0154] Moreover, in the present embodiment, as shown in FIG. 4 andequation (11), the first color data Ri, Gi, Bi are respectivelymultiplied by predetermined coefficients, and the sum of the resultingvalues is found so that the brightness information V is calculated. Inthe human sensitivities, the brightness is recognized differentlydepending on colors due to visual sensitivity characteristics. Forexample, even in the case of the same signal level, a green color isfelt brighter, and a blue color is felt darker. Therefore, by definingthe brightness information as shown in equation (11), it is possible tocalculate and find the brightness information V that is close to humansensitivity.

[0155] Moreover, since the second color correction amount is obtained bymultiplying the first color correction amount by the multiplicationcoefficient k, it is only necessary to use the multiplicationcoefficient k as the data for finding the color correction amount(second color correction amount) corresponding to the brightnessinformation of the first color data. For example, in the conventionalcolor converter shown in FIG. 26, it is proposed that the colorcorrection amounts R1 a, G1 a, B1 a are calculated in association withthe brightness information of the first color data Ri, Gi, Bi. However,as described above, in the arrangement of FIG. 26, since the colorcorrection amounts R1 a, G1 a, B1 a are found on the basis of equation(3), it is necessary to calculate the coefficient matrix (A1ij)corresponding to each of the first color data in association with thebrightness information of the first color data in order to allow thecolor correction amounts to correspond to the first color data. In otherwords, since i=1 to 3 and j=1 to 3 in equation (3), the total 9coefficient data need to be calculated. For this reason, the presentembodiment has an advantage in that it is possible to reduce the amountof data to be calculated in order to obtain the color correction amount(second color correction amount) in association with the brightnessinformation of the first color data.

[0156] Moreover, the present embodiment has been described on thepremise that a hardware configuration is adopted; however, the sequenceof the color-conversion processes shown in the present embodiment may beachieved on a software basis.

[0157] Furthermore, in the above-mentioned embodiment, the first colordata are constituted by three components representing red, green andblue; however, the present invention is easily applicable to a case inwhich the first color data are constituted by not less than four colors,with the same effects. In this case, the brightness information V isfound from color data on the basis of the components of not less thanfour colors.

2. Embodiment 2

[0158] In embodiment 1, the multiplication coefficient calculation means4 is provided with the brightness information calculation means 8, andthe brightness information calculation means 8 calculates the brightnessinformation V from the first color data Ri, Gi, Bi. However, in the casewhere the brightness information V of the first color data ispreliminarily known, it is not necessary for the multiplicationcoefficient calculation means 4 to calculate the brightness informationfrom the first color data, and the multiplication coefficient k may beobtained from the brightness information V that has been preliminarilyknown.

[0159] For example, in the case of a television signal, a video signaland the like, the image signal is sometimes constituted by not signalsof R, G, B, but a luminance signal and a color-difference signal. Insuch a case, for example, in the case where the inputs of the colorconverter are set to signals of R, G, B, after the first color data Ri,Gi, Bi have been calculated from the luminance signal and thecolor-difference signal, the resulting data need to be inputted.However, the luminance signal, as it is, may be used as the brightnessinformation V. Therefore, in this case, the multiplication coefficientcalculation means 4 need not be provided with the brightness informationcalculation means 8, and the multiplication coefficient k may becalculated from the brightness information V (luminance signal) inputtedto the device.

[0160]FIG. 7 is a block diagram showing one example of a configurationof a color converter according to embodiment 2 of the present invention.In this Figure, those elements that are the same as those of FIG. 1 areindicated by the same reference numbers, and the description thereofwill not be repeated. Here, reference numeral 4 b representsmultiplication coefficient calculation means in the present embodiment.

[0161] The brightness information V is inputted to the multiplicationcoefficient calculation means 4 b, and a multiplication coefficient kcorresponding to the value is outputted. The multiplication coefficientcalculation means 4 b may be formed as a look up table in which valuesof the multiplication coefficient k corresponding to the respectivevalues of the brightness information V have been preliminarily stored asaddresses for the brightness information V. Moreover, this may beconstituted by arithmetic circuits.

[0162] As described above, in the case where the brightness informationV of the first color data Ri, Gi, Bi have been preliminarily known, itis not necessary for the multiplication coefficient calculation means 4a to have the brightness information calculation means; thus, it ispossible to simplify the circuit configuration and processes.

3. Embodiment 3

[0163]FIG. 8 is a block diagram showing one example of a configurationof brightness information calculation means 8 in a color converteraccording to embodiment 3 of the present invention. As shown in thisFigure, the brightness information calculation means 8 is formed bymaximum value calculation means 12. Here, the other structures exceptfor the brightness information calculation means 8 of the colorconverter according to the present embodiment are the same as those ofembodiment 1; therefore, the detailed description thereof will not berepeated.

[0164] The first color data Ri, Gi, Bi, inputted to the brightnessinformation calculation means 8, are inputted to the maximum valuecalculation means 12, and the maximum value of Ri, Gi, Bi is outputtedas the brightness information V. In other words, in the presentembodiment, the brightness information is defined as V=MAX (Ri, Gi, Bi).

[0165] In embodiment 1, the respective values of the first color dataare multiplied by predetermined coefficients, and by finding the sum ofthese values, the brightness information V is calculated in a manner soas to become close to human sensitivity (equation (11)). However, noisecomponents contained in the first color data are generated irrespectiveof the human sensitivity, and the influences of the noise components inthe first color data are varied on the basis of the relativerelationship of sizes between the original color data components Rs, Gs,Bs and the noise components Rn, Gn, Bn.

[0166] For example, in both of the cases in which noise componentsRn=20, Gn=20, Bn=40 are added to the original color data componentsRs=200, Gs=50, Bs=50, and in which noise components Rn=20, Gn=20, Bn=40are added to the original color data components Rs=50, Gs=200, Bs=50,the influences of the noise components are the same in a color dataspace. However, the brightness information calculated by the brightnessinformation calculation means in embodiment 1 is different between thesetwo cases. In contrast, in the present embodiment, the brightnessinformation calculated in the brightness information calculation meansforms the same value, that is, V=220, in both of the two cases. Thisfact indicates that in the color converter in the present embodiment,the susceptibility of the brightness information to the influences ofthe noise components in the first color data is correctly represented inthe color data space.

[0167] The degree of the influences of the noise components in the firstcolor data is considered to be mainly dependent on the maximum value ofthe color data components; therefore, even when the multiplicationcoefficient k is found by using the brightness information V=MAX (Ri,Gi, Bi), it is possible to obtain the same effects as embodiment 1.

[0168] Moreover, different from the calculation method of the brightnessinformation by the use of equation (11), the calculation of thebrightness information V=MAX (Ri, Gi, Bi) requires no multiplyingprocesses. In general, multiplying processes impose a great operationload, and in particular, in the case of a hardware configuration, a verylarge circuit scale is required. Therefore, it is very important toeliminate multiplying processes in the calculation of the brightnessinformation, and this makes it possible to reduce the operation load inthe brightness information calculation means in the color converter, andalso to cut the circuit scale.

4. Embodiment 4

[0169] The application of the arrangement shown in FIGS. 1 or 7 makes itpossible to reduce the generation of damaged color in bright colors byaltering the relationship between the multiplication coefficient k andthe brightness information V. FIG. 9 is a graph that indicates oneexample of the relationship between the multiplication coefficient k andbrightness information V to be stored in the look up table 9 in a colorconverter according to embodiment 4 of the present invention. In thefollowing description, except for the relationship between themultiplication coefficient k and the brightness information V, the otherarrangements of the color converter of the present embodiment are thesame as those of embodiment 3 (FIGS. 1 and 8).

[0170] In the first color correction amount calculation means 1, thefirst color correction amounts R1, G1, B1 are calculated by operationsrepresented by the following equation (12): $\begin{matrix}{\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {({A1ij})\begin{bmatrix}{Ri} \\{Gi} \\{Bi}\end{bmatrix}}} & {{Equation}\quad (12)}\end{matrix}$

[0171] In equation (12), the coefficient matrix A1ij has a coefficientrepresented by the following equation (13): $\begin{matrix}{({A1ij}) = \begin{bmatrix}0.2 & {- 0.1} & {- 0.1} \\{- 0.1} & 0.2 & {- 0.1} \\{- 0.1} & {- 0.1} & 0.2\end{bmatrix}} & {{Equation}\quad (13)}\end{matrix}$

[0172] In this case, suppose that data having high brightness, such asRi=230, Gi=20, Bi=20, are inputted as the first color data. In thiscase, the brightness information V is 230, and the multiplicationcoefficient k is 0.4 from FIG. 9. Moreover, the first color correctionamount is represented by R1=42, G1=−21, B1=−21. Here, one decimal isrounded to the nearest whole number. Therefore, the second color data,which are the outputs of the color converter, are represented by Ro=247,Go=12, Bo=12.

[0173] Here, suppose that data, Ri=240, Gi=15, Bi=15, are inputted asthe first color data. In this case, the brightness information V is 240,and the multiplication coefficient k is 0.24 from FIG. 9. Moreover,R1=45, G1=−23 and B1=−23 are obtained. Therefore, the second color dataare represented by Ro=251, Go=9, Bo=9.

[0174] As described above, in the conventional color converter, thevalues of Ro, Go, Bo obtained when Ri=230, Gi=20, Bi=20 are inputted asthe first color data become the same as the values of Ro, Go, Boobtained when Ri=240, Gi=15, Bi=15 are inputted as color data, resultingin damaged color. In contrast, it is confirmed that the color converterof the present embodiment causes no damaged color.

[0175] In the present embodiment, the maximum value of the first colordata Ri, Gi, Bi is used as the brightness information V; however, notlimited to this method, the method for calculating the brightnessinformation V may be carried out by using equation (11) as described in,for example, embodiment 1.

[0176] Moreover, in this case, a look up table is used as the means forfinding the multiplication coefficient k from the brightness informationV; however, the look up table to be used here is achieved by aone-dimensional table with respect to the brightness information V. Inother words, it is not necessary to provide a large capacity look uptable such as a three-dimensional look up table with respect to colordata R, G, B used in the conventional table conversion system.

[0177] Here, the means for finding the corresponding multiplicationcoefficient k from the brightness information V may be constituted byarithmetic circuits or the like. However, the arrangement using the lookup table has an advantage that is not achieved by arithmetic circuits,in that various characteristics are easily achieved by rewriting thecontents of the table without changing the circuit configuration.

[0178] As described above, in accordance with the color converter andcolor converting method according to the present embodiment, in the casewhere the process for enhancing the saturation of color data is carriedout, without the necessity of using any large capacity memory, it ispossible to reduce the generation of damaged color in color data havinghigh brightness.

[0179] Here, the relationship between the brightness information V andthe multiplication coefficient k is not limited to the relationshipshown in FIG. 9, and any relationship which makes the multiplicationcoefficient k small when the value of the brightness information V isgreat may be used with the same effects.

[0180] Moreover, the present embodiment has been described on thepremise that a hardware configuration is adopted; however, the sequenceof the color-conversion processes shown in the present embodiment may beachieved on a software basis.

[0181] Furthermore, in the above-mentioned embodiment, the first colordata are constituted by three components representing red, green andblue; however, the present invention is easily applicable to a case inwhich the first color data are constituted by not less than four colors,with the same effects. In this case, the brightness information V isfound from color data on the basis of the components of not less thanfour colors.

5. Embodiment 5

[0182]FIG. 10 is a block diagram showing one structural examplemultiplication coefficient calculation means 4 in a color converteraccording to embodiment 5 of the present invention. As shown in thisFigure, reference numeral 13 is saturation information calculationmeans, and 9 b is a look up table (LUT). Here, the other structuresexcept for the saturation information calculation means 4 are the sameas those of embodiment 1 (FIG. 1); therefore, the detailed descriptionthereof will not be repeated. In embodiment 1, the multiplicationcoefficient k is calculated by using brightness information ascharacteristic information of the first color data Ri, Gi, Bi; however,in the color converter according to the present embodiment, themultiplication coefficient k is calculated by using saturationinformation as characteristic information of the first color data Ri,Gi, Bi.

[0183] The first color data Ri, Gi, Bi, inputted to the multiplicationcoefficient calculation means 4, is inputted to the saturationinformation calculation means 13. The saturation information calculationmeans 13 calculates saturation information SA that is informationrepresenting the saturation of the first color data Ri, Gi, Bi, andoutputs this to the look up table 9 b.

[0184] The look up table 9 b is formed by a memory and the like, andvalues of the multiplication coefficient k corresponding to the valuesof the saturation information SA are preliminarily stored therein. Thelook up table 9 b extracts a multiplication coefficient k correspondingto the value of inputted saturation information SA from the memory, andoutputs the resulting value. For example, values of the multiplicationcoefficient k that respectively correspond to values of the saturationinformation SA are preliminarily stored in the memory of the look uptable 9 b with the saturation information SA being set in the form ofaddresses; thus, by inputting saturation information SA as a readoutaddress, the corresponding multiplication coefficient k can beoutputted.

[0185] In the second color correction amount calculation means 5, eachof the first color correction amounts R1, G1, B1 is multiplied by themultiplication coefficient k outputted from the look up table 9 b of themultiplication coefficient calculation means 4 so that the second colorcorrection amounts R2, G2, B2 are calculated. Then, the second colorcorrection amounts R2, G2, B2 are respectively added to the first colordata Ri, Gi, Bi by the color correction amount addition means 2 so thatthe second color data Ro, Go, Bo are calculated.

[0186]FIG. 11 is a block diagram showing one structural example ofsaturation information calculation means 13 shown in FIG. 10. In thisFigure, reference numeral 12 b is maximum value calculation means, 14 isminimum value calculation means and 15 is saturation operation means.The first color data Ri, Gi, Bi are inputted to the maximum valuecalculation means 12 b and the minimum value calculation means 14. Themaximum value calculation means 12 b calculates the maximum value MAX1of the first color data Ri, Gi, Bi, and outputs this to the saturationcalculation means 15. The minimum value calculation means 14 calculatesthe minimum value MIN1 of the first color data Ri, Gi, Bi, and outputsthe resulting value to the saturation operation means 15. On the basisof the inputted maximum value MAX1 and minimum value MIN1, thesaturation operation means 15 calculates saturation information SArepresented by the following equation (14) derived from equation (5).

SA=(MAX1−MIN1)/MAX1   Equation (14)

[0187] For example, in the case of Ri=255, Gi=0, Bi=0 in the first colordata, saturation information SA=1.0 is obtained, and in the case ofRi=128, Gi=64, Bi=64 in the first color data, saturation informationSA=0.5 is obtained.

[0188] The following description will discuss the relationship betweenthe multiplication coefficient k and the saturation information SA to bestored in the look up table 9 b in the present embodiment and theeffects thereof. Here, in the following description also, it is assumedthat the first and second color data are represented by integers in arange from 0 to 255, and that first decimal is rounded to the nearestwhole number.

[0189]FIG. 12 is a graph that shows one example of the relationshipbetween the multiplication coefficient k and the saturation informationSA to be stored in the look up table 9 b. In a range from SA=0 toSA=0.3, the multiplication coefficient is set to k=1.0. Moreover, whenSA=1.0, k=0.0, and in a range from SA=0.3 to SA=1.0, k is variedlinearly with respect to SA.

[0190] In the first color correction amount calculation means 1, thefirst color correction amounts R1, G1, B1 are calculated throughoperations represented by the following equation (15). $\begin{matrix}{\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {({A1ij})\begin{bmatrix}{Ri} \\{Gi} \\{Bi}\end{bmatrix}}} & {{Equation}\quad (15)}\end{matrix}$

[0191] Moreover, in equation (15), the coefficient matrix A1ij has acoefficient represented by the following equation (16): $\begin{matrix}{({A1ij}) = \begin{bmatrix}0.2 & {- 0.2} & {- 0.2} \\{- 0.2} & 0.2 & {- 0.2} \\{- 0.2} & {- 0.2} & 0.2\end{bmatrix}} & {{Equation}\quad (16)}\end{matrix}$

[0192] For example, suppose that Ri=255, Gi=128, Bi=128, are inputted asthe first color data. In this case, the saturation Sati of the firstcolor data is 0.5, and the multiplication coefficient k is 0.72 fromFIG. 12. Moreover, from equations (15) and (16), the first correctionamounts are set to R1=0, G1=−51, B1=−51. Therefore, from equation (9),the second color data, which are outputs of the color converter, are setto Ro=255, Go=91, Bo=91. The saturation Sato of the second color data is0.64; thus, it is confirmed that the saturation of the color data ismade higher by the color conversion processes.

[0193] Here, suppose that color data having high saturation, such asRi=255, Gi=26, Bi=26, are inputted as the first color data. In thiscase, the saturation Sati of the first color data is 0.9, and themultiplication coefficient k is 0.14. Moreover, the first correctionamounts are represented by R1=41, G1=−51, B1=−51. Therefore, the secondcolor data are represented by Ro=255, Go=19, Bo=19. The saturation Satoof the second color data is 0.93.

[0194] Here, suppose that data, Ri=255, Gi=51, Bi=51, are inputted asthe first color data. In this case, the saturation Sati of the firstcolor data is 0.8, and the multiplication coefficient k is 0.29.Moreover, the first correction amounts are represented by R1=31, G1=−51and B1=−51. Therefore, the second color data are represented by Ro=255,Go=36, Bo=36. The saturation Sato of the second color data is 0.86.

[0195] As described above, in the conventional color converter, thevalues of Ro, Go, Bo of the second color data, obtained when Ri=255,Gi=26, Bi=26 are inputted as the first color data, become the same asthe values of Ro, Go, Bo of the second color data obtained when Ri=255,Gi=51, Bi=51 are inputted as the first color data, resulting in damagedcolor. In contrast, it is confirmed that the color converter of thepresent embodiment causes no damaged color.

[0196] Here, the relationship between the saturation information SA andthe multiplication coefficient k is not limited to the relationshipshown in FIG. 12, and any relationship which makes the multiplicationcoefficient k small when the value of the saturation information SA isgreat may be used with the same effects.

[0197]FIG. 13 is a graph that shows another example of the relationshipbetween the multiplication coefficient k and the saturation informationSA to be stored in the look up table 9 b. In a range of the saturationinformation from SA=0 to SA=0.7, k=1.0 is set, and when SA=1.0, k=0.0 isset. Moreover, in a range from SA=0.7 to SA=1.0, the value of themultiplication coefficient k is varied linearly with respect to thesaturation information SA.

[0198] In this case also, descriptions are given of the above-mentionedexamples in the same manner. First, when Ri=255, Gi=128, Bi=128, areinputted as the first color data, the saturation Sati of the first colordata is 0.5, and the multiplication coefficient k is 1.0 from FIG. 13.Moreover, since the first correction amounts are set to R1=0, G1=−51,B1=−51, the second color data are set to Ro=255, Go=77, Bo=77. Thesaturation Sato of the second color data is 0.70; thus, it is confirmedthat the saturation of the color data is made higher by the colorconversion processes.

[0199] Next, when data, Ri=255, Gi=26, Bi=26, are inputted as the firstcolor data, the saturation Sati of the first color data is 0.9, and themultiplication coefficient k is 0.34. Moreover, since the firstcorrection amounts are represented by Ri=41, Gi=−51 and Bi=−51, thesecond color data are represented by Ro=255, Go=9, Bo=9. The saturationSato of the second color data is 0.96.

[0200] Moreover, when data, Ri=255, Gi=51, Bi=51, are inputted as thefirst color data, the saturation Sati of the first color data is 0.8,and the multiplication coefficient k is 0.67. Moreover, since the firstcorrection amounts are represented by R1=31, G1=−51 and B1=−51, thesecond color data are represented by Ro=255, Go=17, Bo=17. Thesaturation Sato of the second color data is 0.93.

[0201] In this case also, the values of the second color data Ro, Go, Boare different between cases in which the first color data are set toRi=255, Gi=26, Bi=26, and in which these are set to Ri=255, Gi=51,Bi=51, causing no color damage.

[0202] As clearly indicated by the above-mentioned examples, whencomparison is made between cases in which the relationship of themultiplication coefficient k and the saturation information SA is shownby FIG. 12 and in which the relationship is shown by FIG. 13, the caseof FIG. 12 has greater effects for preventing damaged color in the caseof high saturation in the first color data; however, it has smallereffects for emphasizing the saturation in the color conversion as awhole. In contrast, the case of FIG. 13 has comparatively smallereffects for preventing damaged color; however, it has greater effectsfor emphasizing the saturation.

[0203] Moreover, in this case, a look up table is used as the means forfinding the multiplication coefficient k from the saturation informationSA; however, the look up table to be used here is achieved by aone-dimensional table with respect to the saturation information SA. Inother words, it is not necessary to provide a large capacity look uptable such as a three-dimensional look up table with respect to colordata R, G, B used in the conventional table conversion system.

[0204] Moreover, in the present embodiment, the look up table is used asthe means for finding the corresponding multiplication coefficient kfrom the saturation information SA; however, this means may be formed byusing arithmetic circuits and the like. However, the arrangement usingthe look up table has an advantage that is not achieved by arithmeticcircuits, in that various characteristics are easily achieved byrewriting the contents of the table without changing the circuitconfiguration.

[0205] As described above, in accordance with the color converter andcolor converting method according to the present embodiment, in the casewhere the process for enhancing the saturation of color data is carriedout, without the necessity of using any large capacity memory, it ispossible to reduce the generation of damaged color in color data havinghigh saturation.

[0206] Moreover, the present embodiment has been described on thepremise that a hardware configuration is adopted; however, the sequenceof the color-conversion processes shown in the present embodiment may beachieved on a software basis.

[0207] Furthermore, in the above-mentioned embodiment, the first colordata are constituted by three components representing red, green andblue; however, the present invention is easily applicable to a case inwhich the first color data are constituted by not less than four colors,with the same effects. In this case, the saturation information SA isfound from color data on the basis of the components of not less thanfour colors.

[0208] In addition, in the present embodiment, the saturationinformation SA is found through operations on the basis of theabove-mentioned equation (14); however, the saturation information SAmay be found through other operations by using the maximum value MAX1and the minimum value MIN1 of the first color data Ri, Gi, Bi. It isclear that, for example, even when the saturation information is definedas SA=MAX1−MIN1, the same effects can be obtained, and in this case,since the saturation information SA can be calculated by using onlysubtracting processes, it is possible to greatly reduce the operationamounts, and also to cut the scale of arithmetic circuits forcalculating the saturation information SA.

[0209] Here, in the present embodiment, the multiplication coefficientcalculation means 4 is provided with the saturation informationcalculation means 13, and the brightness information V is calculatedfrom the first color data Ri, Gi, Bi in the saturation informationcalculation means 13. However, in the case where the saturationinformation SA of the first color data has been preliminarily known, thesaturation information SA inputted through an external device may bedirectly inputted to the look up table 9 b so that the multiplicationcoefficient k is calculated. In this case, in an attempt to simplify thecircuit configuration and processes, the multiplication coefficientcalculation means 4 may be designed so as not to include the saturationinformation calculation means 13.

6. Embodiment 6

[0210] Embodiment 6 will discuss one example of a first color correctionamount calculation means in a color conversion circuit in the presentinvention. First, the following description will discuss a basicequation used for obtaining first color correction amounts R1, G1, B1 inthe first color correction amount calculation means according to thepresent embodiment.

[0211] Here, suppose that the first color data components to be inputtedto the first color correction amount calculation means are Ri, Gi, Bithat are signals respectively representing red, green and blue, and thatthe maximum value is α=MAX (Ri, Gi, Bi). In this case, six hue data r,g, b, y, m, c, relating to red, green, blue, yellow, magenta, cyan arerespectively represented by r=Ri−α, g=Gi−α, b=Bi−α and y=β−Bi, m=β−Gi,c=β−Ri.

[0212] FIGS. 14(A) to 14(F) respectively show schematic relationshipsamong the above-mentioned six hues and color hue data y, m, c, r, g, b.As shown in these Figures, the respective hue data are respectivelyassociated with three hues.

[0213] Here, with respect to first operation terms, the following termsare defined: h1r=MIN (y, m), h1y=MIN (r, g), h1g=MIN (c, y), h1c=MIN (g,b), h1b=MIN (m, c) and h1m=MIN (b, r). On the basis of the relationshipshown in FIG. 14, relationships between these first operation terms h1r,h1y, h1g, h1c, h1b, h1m and the above-mentioned six hues areschematically shown as FIGS. 15 (A) to 15(F). These Figures show thateach of the first terms is related to only the specific one hue.

[0214] Moreover, with respect to second operation terms, the followingterms are defined: h2ry=MIN (aq1×h1y, ap1×h1r), h2gy=MIN (aq3×h1y,ap3×h1g), h2gc=MIN (aq4×h1c, ap4×h1g), h2bc=MIN (aq6×h1c, ap6×h1b),h2bm=MIN (aq5×h1m, ap5×h1b) and h2rm=MIN (aq2×h1m, ap2×h1r). In therespective terms, aq1 to aq6 and ap1 to ap6 are predetermined operationcoefficients.

[0215] First, for convenience of description, the following descriptionis given on the assumption that all the values of the operationcoefficients aq1 to aq6 and ap1 to ap6 are set to 1. In this case,second operation terms are respectively defined as follows: h2ry=MIN(h1y, h1r), h2gy=MIN (h1y, h1g), h2gc=MIN (h1c, h1g), h2bc=MIN (h1c,h1b), h2bm=MIN (h1m, h1b), and h2rm=MIN (h1m, h1r). In this case, on thebasis of the relationship shown in FIG. 15, relationships between thesesecond operation terms h2ry, h2gy, h2gc, h2bc, h2bm, h2rm and theabove-mentioned six hues are schematically shown as FIGS. 16(A) to16(F). These Figures show that each of the second terms is related toonly the specific intermediate area (inter-hue area) between hues. Inother words, h2ry, h2gy, h2gc, h2bc, h2bm and h2rm are respectivelyrelated to a change in intermediate area between six hues, that is, redto yellow, yellow to green, green to cyan, cyan to blue, blue tomagenta, and magenta to red.

[0216] Next, the following description will discuss a case in which theoperation coefficients aq1 to aq6 and ap1 to ap6 in the second operationterms have respective predetermined values. FIGS. 17(A) to 17(F) arediagrams that schematically show the relationships between six hues andthe second operation terms in the case where the values of the operationcoefficients aq1 to aq6 and ap1 to ap6 in the respective secondoperation terms hry, hrm, hgy, hgc, hbm and hbc are varied. In theseFigures, broken lines a1 to a6 show cases in which aq1 to aq6 are set tovalues that are respectively greater than ap1 to ap6. In contrast,broken lines b1 to b6 show cases in which ap1 to ap6 are set to valuesthat are respectively greater than aq1 to aq6. In this case also, theseFigures show that each of the second terms is related to only thespecific intermediate area between hues.

[0217] For example, with respect to red to yellow, only h2ry=MIN(aq1×h1y, ap1×h1r) is the effective second operation term; however, forexample, in the case where a ratio of aq1 and ap1 is set to 2:1, therelationship as indicated by broken line a1 in FIG. 22(A) is prepared sothat an operation term having a peak value that relates to the red sideis prepared; thus, the operation term is made particularly effective inan area close to red between the hues from red to yellow. In contrast,in the case where a ratio of aq1 and ap1 is set to 1:2, the relationshipas indicated by broken line b1 in FIG. 22(A) is prepared so that anoperation term having a peak value that relates to the yellow side isprepared; thus, the operation term is made particularly effective in anarea close to yellow between the hues from red to yellow. In the samemanner, by respectively changing aq3 and ap3 in h2gy with respect toyellow to green, aq4 and ap4 in h2gc with respect to green to cyan, aq6and ap6 in h2bc with respect to cyan to blue, aq5 and ap5 in h2bm withrespect to blue to magenta, and aq2 and ap2 in h2rm with respect tomagenta to red, it is possible to change particularly effective areaseven at areas between the respective hues.

[0218] FIGS. 18(a) and (b) collectively show the correspondingrelationships between the six hues and inter-hue areas and the effectiveoperation terms for these. FIG. 18(a) shows the correspondingrelationships between six hues and the first operation terms, and FIG.18(b) shows the corresponding relationships between the inter-hue areasand the second operation terms.

[0219] Here, the basic equation, which is used for finding the firstcolor correction amounts R1, G1, B1 in the first color correction amountcalculation means of the color conversion circuit according to thepresent embodiment, is given as the following equation (17):$\begin{matrix}{\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {({Fij})\begin{bmatrix}{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc} \\\alpha\end{bmatrix}}} & {{Equation}\quad (17)}\end{matrix}$

[0220] Herein, Fij is a coefficient matrix with i=1 to 3 and j=1 to 13.

[0221] By setting the operation expression of the first color correctionamounts to equation (17), the coefficient relating to an operation termthat is effective to a hue or an area between hues to be adjusted ischanged so that it becomes possible to correct only the target hue orpredetermined area between hues in an independent manner.

[0222] Moreover, by changing the operation coefficients aq1 to aq6 andap1 to ap6 respectively, it is possible to change an area which makesthe respective second operation terms particularly effective in eachinter-hue areas without causing any adverse effect to the other hues. Inother words, it becomes possible to correct the degree of a change inthe inter-hue area in an independent manner.

[0223] Therefore, it becomes possible to flexibly change the conversioncharacteristics in the color-conversion process by finding the firstcolor correction amount by using the operations of equation (17).

[0224] Here, in accordance with the definition of equation (17), matrixoperations need to be carried out with respect to thirteen operationterms including the first operation terms, the second operation termsand the minimum value α of the first color data. Consequently, a numberof multiplying processes have to be carried out so as to realize thissystem. As described above, multiplying processes impose a high load,and make the circuit scale greater, in particular in, the case of ahardware configuration, resulting in a large circuit scale so as tocarry out operations of equation (17).

[0225] For this reason, in the present embodiment, the operations withrespect to equation (17) are carried out in a manner so as to excludedata the value of which is zero from the first operation terms and thesecond operation terms; thus, the first color correction amountcalculation means of the present embodiment makes it possible to reducethe operation load and also to cut the circuit scale.

[0226] The following description will discuss the first operation termsand the second operation terms the value of which is set to zero.Moreover, consideration is further given to six hues. For example,supposing that the first color data, Ri, Gi, Bi, exhibit a red color,equations, r=W and g=b=0, hold with W being a constant. Therefore,y=m=W, and c=0. In this case, in the first operation terms, h1r=MIN (y,m)=W hold so that all the other five terms in the first operation termsbecome zero, as shown in FIG. 15. Moreover, in this case, it is clearthat all the second operation terms are zero, and this fact is alsoshown by FIG. 17. In other words, with respect to red, only theeffective operation term is h1r=MIN (y, m). In the same manner, thefollowing terms form only the effective first operation terms: withrespect to green, h1g=MIN (c, y), with respect to blue, h1b=MIN (m, c),with respect to cyan, h1c=MIN (g, b), with respect to magenta, h1m=MIN(b, r), and with respect to yellow, h1y=MIN (r, g).

[0227] Next, consideration will be given to intermediate areas(inter-hue areas) between six hues. For example, with respect to thearea from red to yellow, b=c=0 holds as shown in FIG. 14. Therefore, asshown in FIG. 15, in the first operation terms, the terms, h1g=MIN (c,y), h1c=MIN (g, b), h1b=MIN (m, c) and h1m=MIN (b, r), are set to zero,and only the terms, h1r=MIN (y, m) and h1y=MIN (r, g), are effectiveoperation terms. As a result, as shown in FIG. 17, only the term,h2ry=MIN (h1y, h1r), serves as an effective operation term in the secondoperation terms, the other five terms except for this become zero. Inthe same manner, the following terms respectively form the effectiveoperation terms: with respect to yellow to green, h1y, h1g, h2gy, withrespect to green to cyan, h1g, h1c, h2gc, with respect to cyan to blue,h1b, h1c, h2bc, with respect to blue to magenta, h1b, h1m, h2bm, andwith respect to magenta to red, h1m, h1r, h2rm.

[0228] As described above, the number of operation terms in equation(17) that become effective simultaneously is at most four consisting ofone of the first operation terms h1r, h1g and h1b, one of h1y, h1m andh1c, one of the second operation terms h2ry, h2gy, h2gc, h2bc, h2bm andh2rm, and the minimum value α of the first color data Ri, Gi and Bi.

[0229] In other words, by effectively utilizing the characteristics ofhue data, the polynomial data (the first operation terms, secondoperation terms, α) of equation (17) can be reduced to four effectivedata among 13 data, when only the image data of each pixel has beentaken into consideration.

[0230]FIG. 19 is a block diagram showing one example of a configurationof first color correction amount calculation means 1 in a colorconverter according to embodiment 6 of the present invention. In thisFigure, reference numeral 16 is an αβ calculator which calculates themaximum value β=MAX (Ri, Gi, Bi) and the minimum value α=MIN (Ri, Gi,Bi) of the inputted first color data Ri, Gi, Bi, and outputs theresulting values, and which also generates an identification code S1 forspecifying data having the maximum value and data having the minimumvalue, and outputs the code; 17 is a hue data calculator whichcalculates hue data r, g, b, y, m, c from the first color data Ri, Gi,Bi and the output from the αβ calculator; 18 is a polynomial computingunit; 6 b is a matrix computing unit; and 7 b is a coefficientgenerator.

[0231] Moreover, FIG. 20 is a block diagram showing one structuralexample of the polynomial computing unit 18 shown in FIG. 19. In thisfigure, reference numeral 19 is a zero eliminator which eliminates datathat become zero among the inputted hue data, 20 a, 20 b and 20 c areminimum value selectors which select the minimum value of data inputtedfrom the zero eliminator 19, and output the resulting value, 22 is anoperation coefficient generator which generates and outputs operationcoefficients aq and ap on the basis of the identification code S1 fromthe αβ calculator, and 21 a and 21 b are computing units which carry outmultiplying processes between the operation coefficients aq and ap fromthe above-mentioned operation coefficient generator 22 and the outputsof the minimum value selectors 20 a and 20 b.

[0232] Next, the following description will discuss operations of theabove-mentioned first color correction amount calculation means. Thefirst color data Ri, Gi, Bi, inputted to the first color correctionamount calculation means, are sent to the αβ calculator 16 and the huedata calculator 17. The αβ calculator 16 calculates the maximum value βand the minimum value α of the first color data Ri, Gi, Bi, and outputsthe resulting values, and also generates and outputs an identificationcode S1 that specifies data forming the maximum value and data formingthe minimum value from the first color data Ri, Gi, Bi.

[0233] The hue data calculator 17 uses the inputted first color data Ri,Gi, Bi, and the inputted maximum value β and the minimum value α fromthe above-mentioned αβ calculator 16, and carries out subtractionprocesses of r=Ri−α, g=Gi−α, b=Bi−α and y=β−Bi, m=β−Gi, c=β−Ri, therebyoutputting six hue data, r, g, b, y, m and c.

[0234] At this time, the maximum value β and the minimum value αcalculated in the αβ calculator 16 are represented by β=MAX (Ri, Gi, Bi)and α=MIN (Ri, Gi, Bi), and since the six hue data, r, g, b, y, m, c,calculated in the hue data calculator 17 are obtained through thesubtraction processes of r=Ri−α, g=Gi−α, b=Bi−α and y=β−Bi, m=β−Gi,c=β−Ri, the resulting six hue data are allowed to have a characteristicin which at least two terms thereof become zero.

[0235] For example, in the case where the maximum value β is Ri and theminimum value α is Gi (β=Ri, α=Gi), the above-mentioned subtractionprocesses yield g=0 and c=0. Moreover, in the case where the maximumvalue β is Ri and the minimum value α is Bi (β=Ri, α=Bi), theabove-mentioned subtraction processes yield b=0 and c=0. In other words,depending on the combinations of Ri, Gi, Bi that form the maximum valueand the minimum value, at least one of r, g, b and one of y, m, c, thatis, the total two values, become zero.

[0236] Therefore, it can be said that the identification code S1,outputted from the above-mentioned αβ calculator 16, specifies data thatbecome zero among six hue data. This identification code S1 generatessix kinds of values depending on which values of Ri, Gi, Bi the maximumvalue β and the minimum value α take. FIG. 21 is a diagram that showsthe corresponding relationships among the value of the identificationcode S1, the maximum value β and the minimum value α in the first colordata Ri, Gi, Bi and the hue data that become zero at that time. Here,the value of the identification code S1 in the Figure shows one example,and not limited to the specific value, another value may be used.

[0237] Six hue data, r, g, b and y, m, c, outputted from the hue datacalculator 17, are sent to the polynomial computing unit 18. Moreover,the identification code S1, outputted from the above-mentioned αβcalculator 16, is also inputted to the polynomial computing unit 18.

[0238] Referring to FIG. 20, the following description will discuss theoperation of the polynomial computing unit 18. In the polynomialcomputing unit 18, six hue data from the hue data calculator 17 and theidentification code S1 from the αβ calculator are inputted to the zeroeliminator 19. On the basis of the identification code S1, the zeroeliminator 19 outputs two data Q1, Q2 that are not zero among r, g, b,and two data P1, P2 that are not zero among y, m, c. Q1, Q2, P1 and P2are determined as shown in FIG. 22. For example, in the case ofidentification code S1=0, as shown in FIG. 22, outputs are Q1=r, Q2=b,P1=m and P2=y.

[0239] Here, in the same manner as FIG. 21, the value of theidentification code S1 in the FIG. 22 shows one example, and not limitedto the specific value, another value may be used.

[0240] The minimum value selector 20 a selects the minimum value T4=MIN(Q1, Q2) of the output data Q1, Q2 outputted from the above-mentionedzero eliminator 19, and outputs the resulting value, and the minimumvalue selector 20 b selects the minimum value T2=MIN (P1, P2) of theoutput data P1, P2 outputted from the above-mentioned zero eliminator19, and outputs the resulting value. As described above, Q1, Q2 are twodata that are not zero among r, g, b; consequently, T4 forms aneffective operation term of the first operation terms h1y, h1m, h1c inequation (17). In the same manner, P1, P2 are two data that are not zeroamong y, m, c; consequently, T2 forms an effective operation term of thefirst operation terms h1r, h1g, h1b in equation (17).

[0241] Moreover, the identification code S1 is inputted from theabove-mentioned αβ calculator 16 to the operation coefficient generator22, and the operation coefficient generator 22 generates operationcoefficients aq and ap in accordance with the value of theidentification code S1, and outputs the resulting coefficients to thecomputing units 21 a, 21 b. The computing units 21 a and 21 b carry outcalculations of aq×T4 and ap×T2 on the effective first operation termsT4 and T2, and output the resulting values to the minimum value selector20 c. Then, the minimum value selector 20 c selects the minimum valueT5=MIN (aq×T4, ap×T2) from the outputs of the computing units 21 a and21 b, and outputs the resulting values. As described above, T4 and T2are the first operation terms that are effective in equation (17);consequently, T5 =(aq×T4, ap×T2) form the second operation terms thatare effective in equation (17).

[0242] In other words, the operation coefficients aq and ap, outputtedfrom the operation coefficient generator 22, correspond to the operationcoefficients aq1 to aq6 and ap1 to ap6 that are used for calculations ofthe second operation terms h2ry, h2gy, h2gc, h2bc, h2bm, h2rm inequation (17). On the basis of the identification code S1, the operationcoefficient generator 22 determines the second operation terms that areeffective, and extracts the corresponding operation coefficients aq andap from aq1 to aq6 and ap1 to ap6, and outputs the resultingcoefficients.

[0243] As described above, T2, T4 and T5 are outputted from thepolynomial computing unit 18 as polynomial data. Further, T2, T4 and T5are sent to the matrix computing unit 6 b. Moreover, the minimum value αof the first color data Ri, Gi, Bi, obtained by the αβ calculator 16, isalso inputted to the matrix computing unit 6 b.

[0244] The coefficient generator 7 b determines the first operationterms and the second operation terms that are effective on the basis ofthe identification code S1, and generates the operation coefficient Uijformed by extracting elements corresponding to these from the operationmatrix Fij shown in equation (17), and outputs this to the matrixcomputing unit 6 b.

[0245] The matrix computing unit 6 b, which has received the polynomialdata T2, T4, T5 from the polynomial computing unit 18, the minimum valueα of the first color data from the αβ calculator 16, and the coefficientmatrix Uij from the coefficient generator 7 b, as inputs, carries outoperations of the following equation (18), and outputs the first colorcorrection amounts R1, G1, B1. $\begin{matrix}{\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {({Uij})\begin{bmatrix}{T2} \\{T4} \\{T5} \\\alpha\end{bmatrix}}} & {{Equation}\quad (18)}\end{matrix}$

[0246] With respect to equation (18), in Uij, i=1 to 3 and j=1 to 4.

[0247] As described above, equation (18) represents matrix operationsconsisting of the first operation terms and the second operation termsthat are effective (not zero) in equation (17), the minimum value α ofthe first color data, and coefficient matrix elements corresponding tothese, and makes it possible to provide the same operation results asequation (17).

[0248] Here, FIG. 23 is a block diagram showing one portion of thestructure of the matrix computing unit 6 b, and shows a structure inwhich R1 of the first color correction amounts is calculated andoutputted. In this Figure, reference numerals 10 d to 10 g aremultipliers and 11 c to 11 e are adders.

[0249] The multipliers 10 d to 10 g receive the polynomial data T2, T4,T5 from the polynomial computing unit 18, the minimum value α from theαβ calculator 16 and the coefficient matrix Uij from the coefficientgenerator 7 b, as inputs, and outputs the respective products.

[0250] The adders 11 c and 11 d receive the products that are outputsfrom the respective multipliers 10 d to 10 g as inputs, add these inputdata, and output the sum. The adder 11 e adds data from the adders 11 cand 11 d, and outputs the sum as the first color correction amount R1.

[0251] As also indicated by equation (18), the first color correctionamounts R1, G1, B1 can be respectively calculated by using one of thearrangements of FIG. 23, by selecting the elements of the coefficientmatrix Uij. Here, for example, by using the three arrangements of FIG.23, the calculations of R1, G1, B1 may be carried out through parallelprocesses; thus, it becomes possible to carry out high-speed matrixoperations.

[0252] As described above, in accordance with the first color correctionamount calculation means according to the present embodiment, thirteenpolynomial data in the matrix operations of equation (17) (the firstoperation terms, second operation terms, and minimum value α of thefirst color data) are reduced to four effective polynomial data so thatthe first color correction amounts R1, G1, B1 can be calculated by usingequation (18).

[0253] Therefore, in comparison with a case in which matrix operationsof equation (17) are actually carried out, it becomes possible togreatly reduce the number of the operations. Thus, it becomes possibleto greatly reduce the operation load, and to greatly cut the circuitscale particularly in the case of a hardware configuration.

[0254] Moreover, since the operations of the first color correctionamounts are basically carried out on the basis of equation (17), it ispossible to carry out a correction process on only a target hue or apredetermined area between hues in an independent manner, and also tocorrect the degree of a change in the area between hues independently,as has been described earlier. In other words, it is possible toflexibly change conversion characteristics.

[0255] Here, as described above, depending on combinations of the firstcolor data Ri, Gi, Bi, at least not less than two values of the hue datar, g, b, y, m, c are set to zero. In other words, there are sometimescases in which not less than three of six hue data become zero. However,FIGS. 21 or 22 does not show a case in which not less than three huedata become zero. In the case where not less than three of hue databecome zero, the following processes may be carried out.

[0256] For example, in the case of Ri>Gi=Bi, since β=Ri and α=Gi, Bi,g=b=c=0; thus, there might be a case in which three of the hue databecome zero. At this time, as shown in FIG. 21, this case corresponds toboth of the cases of the identification codes S1=0 and S1=1. However, ineither of the cases of S1=0 and S2=1, the same operation results areobtained depending on combinations of Q1, Q2, P1, P2 in FIG. 22 so thatboth of the cases can provide desired operation results, that is,T2=h1r=MIN (y, m) and T4=T5=0. Here, the same is true to othercombinations which set three of the six hue data to zero.

[0257] Moreover, in the case of Ri=Gi=Bi, that is, all the six hue dataare zero, as shown in FIG. 21, these cases correspond to all theidentification codes S1=0 to 5. In this case also, any of theidentification codes S1=0 to 5 makes it possible to provide desiredoperation results T2=T4=T5=0.

[0258] In other words, in the case where not less than three of hue databecome zero, desired one of a plurality of corresponding identificationcodes may be selected. Here, any selection method may be used. It is ofcourse possible to provide an arrangement in which identification codesthat correspond to respective cases which set not less than three of thehue data to zero are prepared.

[0259] Additionally, the present embodiment has been described on thepremise that a hardware configuration is adopted; however, the sequenceof the color-conversion processes shown in the present embodiment may beachieved on a software basis.

[0260] While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

1. A color converter which carries out color correction on first colordata to convert to second color data corresponding to said first colordata, comprising: first color correction amount calculation means (1)for calculating a first color correction amount on the basis of saidfirst color data by using a matrix computing system; multiplicationcoefficient calculation means (4) for calculating a multiplicationcoefficient on the basis of characteristic information of said firstcolor data; second color correction amount calculation means (5) forcalculating a second color correction amount by multiplying said firstcolor collection amount by said multiplication coefficient; and colorcorrection amount addition means (2) for calculating said second colordata by adding said second color correction amount to said first colordata.
 2. The color converter according to claim 1, wherein thecharacteristic information of said first color data is brightness. 3.The color converter according to claim 2, wherein the value of saidmultiplication coefficient calculated by said multiplication coefficientcalculation means (4) becomes smaller as said brightness becomes smallerthan a predetermined value.
 4. The color converter according to claim 2,wherein the value of said multiplication coefficient calculated by saidmultiplication coefficent calculation means (4) becomes smaller as saidbrightness becomes larger than a predetermined value.
 5. The colorconverter according to claim 1, wherein the characteristic informationof said first color data is saturation.
 6. The color converter accordingto claim 5, wherein the value of said multiplication coefficientcalculated by said multiplication coefficient calculation means (4)becomes smaller as said saturation becomes higher than a predeterminedvalue.
 7. The color converter according to claim 1, further comprising:characteristic information calculation means (8, 13) for calculatingsaid characteristic information on the basis of said first color data.8. The color converter according to claim 7, wherein said characteristicinformation calculated by said characteristic information calculationmeans (8, 13) is brightness of said first color data, and saidbrightness is calculated as a sum of values obtained by multiplying therespective components of said first color data by predeterminedcoefficients.
 9. The color converter according to claim 7, wherein saidcharacteristic information calculated by said characteristic informationcalculation means (8, 13) is brightness of said first color data, andsaid brightness is calculated as the maximum value of the components ofsaid first color data.
 10. The color converter according to claim 7,wherein said characteristic information calculated by saidcharacteristic information calculation means (8, 13) is saturation ofsaid first color data, and said saturation is calculated on the basis ofa difference between the maximum value of the components of said firstcolor data and the minimum value of the components of said first colordata.
 11. The color converter according to claim 1, wherein saidmultiplication coefficient calculation means (4) includes a look uptable (9, 9 b) storing said multiplication coefficient corresponding tosaid characteristic information.
 12. The color converter according toclaim 1, wherein said first color data and said first color correctionamounts are respectively Ri, Gi, Bi and R1, G1, B1 corresponding tothree primary color signals of red, green and blue, and said first colorcorrection calculation means (1) includes: maximum value/minimum valuecalculation means (16) for calculating the minimum value α and themaximum value β of said first color data; hue data calculation means(17) for calculating six hue data: r=Ri−α, g=Gi−═, b=Bi−α, y=β−Ri,m=β−Gi and c=β−Ri, respectively relating to red, green, blue, yellow,magenta and cyan, from said first color data and said minimum value αand maximum value β calculated by said maximum value/minimum valuecalculation means; effective operation term calculation means (18) forcalculating, by using said hue data and a predetermined coefficients ap1to ap6 and aq1 to aq6, a first effective operation term T2 having only avalue which is not zero among h1r=MIN (y, m), h1g=MIN (c, y) and h1b=MIN(m, c) or a zero value when all the h1r, h1g and h1b are zero, a secondeffective operation term T4 having only a value which is not zero amongh1y=MIN (r, g), h1c=MIN (g, b) and h1m=MIN (b, r) or a zero value whenall the h1y, h1c and h1m are zero, and a third effective operation termT5 having only a value which is not zero among h2ry=MIN (aq1×h1y,ap1×h1r), h2rm=MIN (aq2×h1m, ap2×h1r), h2gy=MIN (aq3×h1y, ap3×h1g),h2gc=MIN (aq4×h1c, ap4×h1g), h2bm=MIN (aq5×h1m, ap5×h1b) and h2bc=MIN(aq6×h1c, ap6×h1b) or a zero value when all the h2ry, h2rm, h2gy, h2gc,h2bm and h2bc are zero; coefficient generation means (7 b) forcalculating a coefficient matrix Uij on the basis of said minimum valueα and maximum value β calculated by said maximum value/minimum valuecalculation means; and matrix operation means (6 b) for carrying out thefollowing matrix operation: $\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {({Uij})\begin{bmatrix}{T2} \\{T4} \\{T5} \\\alpha\end{bmatrix}}$

on the basis of said first effective operation term T2, second effectiveoperation term T4 and third effective operation term T5, calculated bysaid operation term calculation means, said minimum value α calculatedby said maximum value/minimum value calculation means and thecoefficient matrix Uij calculated by said coefficient generation means,thereby calculating said first color correction amounts R1, G1, B1. 13.A color converting method which carries out color correction on firstcolor data to convert to second color data corresponding to said firstcolor data, comprising the steps of: (a) calculating a first colorcorrection amount, on the basis of said first color data by using amatrix computing system; (b) calculating a multiplication coefficient onthe basis of characteristic information of said first color data; (c)calculating a second color correction amount by multiplying said firstcolor collection amount by said multiplication coefficient; and (d)calculating said second color data by adding said second colorcorrection amount to said first color data.
 14. The color convertingmethod according to claim 13, wherein the characteristic information ofsaid first color data is brightness.
 15. The color converting methodaccording to claim 14, wherein the value of said multiplicationcoefficient calculated in said step (b) becomes smaller as saidbrightness becomes smaller than a predetermined value.
 16. The colorconverting method according to claim 14, wherein the value of saidmultiplication coefficient calculated in said step (b) becomes smalleras said brightness becomes larger than a predetermined value.
 17. Thecolor converting method according to claim 13, wherein thecharacteristic information of said first color data is saturation. 18.The color converting method according to claim 17, wherein the value ofsaid multiplication coefficient calculated in said step (b) becomessmaller as said saturation becomes larger than a predetermined value.19. The color converting method according to claim 13, furthercomprising the step of: (e) calculating said characteristic informationon the basis of said first color data.
 20. The color converting methodaccording to claim 19, wherein said characteristic informationcalculated in said step (e) is brightness of said first color data, andsaid brightness is calculated as a sum of values obtained by multiplyingthe respective components of said first color data by predeterminedcoefficients.
 21. The color converting method according to claim 19,wherein said characteristic information calculated in said step (e) isbrightness of said first color data, and said brightness is calculatedas the maximum value of the components of said first color data.
 22. Thecolor converting method according to claim 19, wherein saidcharacteristic information calculated in said step (e) is saturation ofsaid first color data, and said saturation is calculated on the basis ofa difference between the maximum value of the components of said firstcolor data and the minimum value of the components of said first colordata.
 23. The color converting method according to claim 13, whereinsaid first color data and said first color correction amounts arerespectively Ri, Gi, Bi and R1, G1, B1 corresponding to three primarycolor signals of red, green and blue, and said step (c) includes thesteps of: (f) calculating the minimum value α and the maximum value β ofsaid first color data; (g) calculating six hue data: r=Ri−α, g=Gi−α,b=Bi−α, y=β−Ri, m=β−Gi and c=β−Ri, respectively relating to red, green,blue, yellow, magenta and cyan, from said first color data and saidminimum value α and maximum value β calculated in said step (f); (h)calculating, by using said hue data calculated in said step (g) and apredetermined coefficients ap1 to ap6 and aq1 to aq6, a first effectiveoperation term T2 having only a value which is not zero among h1r=MIN(y, m), h1g=MIN (c, y) and h1b=MIN (m, c) or a zero value when all theh1r, h1g and h1b are zero, a second effective operation term T4 havingonly a value which is not zero among h1y=MIN (r, g), h1c=MIN (g, b) andh1m=MIN (b, r) or a zero value when all the h1y, h1c and h1m are zero,and a third effective operation term T5 having only a value which is notzero among h2ry=MIN (aq1×h1y, ap1×h1r), h2rm=MIN (aq2×h1m, ap2×h1r), h 2gy=MIN (aq3×h1y, ap3×h1g), h2gc=MIN (aq4×h1c, ap4×h1g), h2bm=MIN(aq5×h1m, ap5×h1b) and h2bc=MIN (aq6×h1c, ap6×h1b) or a zero value whenall the h2ry, h2rm, h2gy, h2gc, h2bm and h2bc are zero; (i) calculatinga coefficient matrix Uij on the basis of said α and β calculated in saidstep (f); and (j) carrying out the following matrix operation:$\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {({Uij})\begin{bmatrix}{T2} \\{T4} \\{T5} \\\alpha\end{bmatrix}}$

on the basis of said first effective operation term T2, second effectiveoperation term T4 and third effective operation term T5 calculated insaid step (h), said minimum value α calculated in said step (f) and thecoefficient matrix Uij calculated in said step (i), thereby calculatingsaid first color correction amounts R1, G1, B1.